item_cmpfunc.h

#ifndef ITEM_CMPFUNC_INCLUDED
#define ITEM_CMPFUNC_INCLUDED
/* Copyright (c) 2000, 2015, Oracle and/or its affiliates.
   Copyright (c) 2009, 2016, MariaDB

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; version 2 of the License.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA */


/* compare and test functions */

#ifdef USE_PRAGMA_INTERFACE
#pragma interface			/* gcc class implementation */
#endif

#include "thr_malloc.h"                         /* sql_calloc */
#include "item_func.h"             /* Item_int_func, Item_bool_func */
#define PCRE_STATIC 1             /* Important on Windows */
#include "pcre.h"                 /* pcre header file */

extern Item_result item_cmp_type(Item_result a,Item_result b);
inline Item_result item_cmp_type(const Item *a, const Item *b)
{
  return item_cmp_type(a->cmp_type(), b->cmp_type());
}
inline Item_result item_cmp_type(Item_result a, const Item *b)
{
  return item_cmp_type(a, b->cmp_type());
}
class Item_bool_func2;
class Arg_comparator;

typedef int (Arg_comparator::*arg_cmp_func)();

typedef int (*Item_field_cmpfunc)(Item *f1, Item *f2, void *arg); 

class Arg_comparator: public Sql_alloc
{
  Item **a, **b;
  Item_result m_compare_type;
  CHARSET_INFO *m_compare_collation;
  arg_cmp_func func;
  Item_func_or_sum *owner;
  bool set_null;                   // TRUE <=> set owner->null_value
  Arg_comparator *comparators;   // used only for compare_row()
  double precision;
  /* Fields used in DATE/DATETIME comparison. */
  THD *thd;
  Item *a_cache, *b_cache;         // Cached values of a and b items
                                   //   when one of arguments is NULL.
  int set_compare_func(Item_func_or_sum *owner, Item_result type);
  int set_cmp_func(Item_func_or_sum *owner_arg, Item **a1, Item **a2);

  int compare_temporal(enum_field_types type);
  int compare_e_temporal(enum_field_types type);

public:
  /* Allow owner function to use string buffers. */
  String value1, value2;

  Arg_comparator(): m_compare_type(STRING_RESULT),
    m_compare_collation(&my_charset_bin),
    set_null(TRUE), comparators(0), thd(0),
    a_cache(0), b_cache(0) {};
  Arg_comparator(Item **a1, Item **a2): a(a1), b(a2),
    m_compare_type(STRING_RESULT),
    m_compare_collation(&my_charset_bin),
    set_null(TRUE), comparators(0), thd(0),
    a_cache(0), b_cache(0) {};

public:
  inline int set_cmp_func(Item_func_or_sum *owner_arg,
			  Item **a1, Item **a2, bool set_null_arg)
  {
    set_null= set_null_arg;
    return set_cmp_func(owner_arg, a1, a2);
  }
  inline int compare() { return (this->*func)(); }

  int compare_string();		 // compare args[0] & args[1]
  int compare_real();            // compare args[0] & args[1]
  int compare_decimal();         // compare args[0] & args[1]
  int compare_int_signed();      // compare args[0] & args[1]
  int compare_int_signed_unsigned();
  int compare_int_unsigned_signed();
  int compare_int_unsigned();
  int compare_row();             // compare args[0] & args[1]
  int compare_e_string();	 // compare args[0] & args[1]
  int compare_e_real();          // compare args[0] & args[1]
  int compare_e_decimal();       // compare args[0] & args[1]
  int compare_e_int();           // compare args[0] & args[1]
  int compare_e_int_diff_signedness();
  int compare_e_row();           // compare args[0] & args[1]
  int compare_real_fixed();
  int compare_e_real_fixed();
  int compare_datetime()   { return compare_temporal(MYSQL_TYPE_DATETIME); }
  int compare_e_datetime() { return compare_e_temporal(MYSQL_TYPE_DATETIME); }
  int compare_time()       { return compare_temporal(MYSQL_TYPE_TIME); }
  int compare_e_time()     { return compare_e_temporal(MYSQL_TYPE_TIME); }

  Item** cache_converted_constant(THD *thd, Item **value, Item **cache,
                                  Item_result type);
  static arg_cmp_func comparator_matrix [6][2];
  inline bool is_owner_equal_func()
  {
    return (owner->type() == Item::FUNC_ITEM &&
           ((Item_func*)owner)->functype() == Item_func::EQUAL_FUNC);
  }
  Item_result compare_type() const { return m_compare_type; }
  CHARSET_INFO *compare_collation() const { return m_compare_collation; }
  Arg_comparator *subcomparators() const { return comparators; }
  void cleanup()
  {
    delete [] comparators;
    comparators= 0;
  }
  friend class Item_func;
};


class SEL_ARG;
struct KEY_PART;

class Item_bool_func :public Item_int_func
{
protected:
  /*
    Build a SEL_TREE for a simple predicate
    @param  param       PARAM from SQL_SELECT::test_quick_select
    @param  field       field in the predicate
    @param  value       constant in the predicate
    @return Pointer to the tree built tree
  */
  virtual SEL_TREE *get_func_mm_tree(RANGE_OPT_PARAM *param,
                                     Field *field, Item *value)
  {
    DBUG_ENTER("Item_bool_func::get_func_mm_tree");
    DBUG_ASSERT(0);
    DBUG_RETURN(0);
  }
  /*
    Return the full select tree for "field_item" and "value":
    - a single SEL_TREE if the field is not in a multiple equality, or
    - a conjuction of all SEL_TREEs for all fields from
      the same multiple equality with "field_item".
  */
  SEL_TREE *get_full_func_mm_tree(RANGE_OPT_PARAM *param,
                                  Item_field *field_item, Item *value);
  /**
    Test if "item" and "value" are suitable for the range optimization
    and get their full select tree.

    "Suitable" means:
    - "item" is a field or a field reference
    - "value" is NULL                (e.g. WHERE field IS NULL), or
      "value" is an unexpensive item (e.g. WHERE field OP value)

    @param item  - the argument that is checked to be a field
    @param value - the other argument
    @returns - NULL if the arguments are not suitable for the range optimizer.
    @returns - the full select tree if the arguments are suitable.
  */
  SEL_TREE *get_full_func_mm_tree_for_args(RANGE_OPT_PARAM *param,
                                           Item *item, Item *value)
  {
    DBUG_ENTER("Item_bool_func::get_full_func_mm_tree_for_args");
    Item *field= item->real_item();
    if (field->type() == Item::FIELD_ITEM && !field->const_item() &&
        (!value || !value->is_expensive()))
      DBUG_RETURN(get_full_func_mm_tree(param, (Item_field *) field, value));
    DBUG_RETURN(NULL);
  }
  SEL_TREE *get_mm_parts(RANGE_OPT_PARAM *param, Field *field,
                         Item_func::Functype type, Item *value);
  SEL_TREE *get_ne_mm_tree(RANGE_OPT_PARAM *param,
                           Field *field, Item *lt_value, Item *gt_value);
  virtual SEL_ARG *get_mm_leaf(RANGE_OPT_PARAM *param, Field *field,
                               KEY_PART *key_part,
                               Item_func::Functype type, Item *value);
public:
  Item_bool_func(THD *thd): Item_int_func(thd) {}
  Item_bool_func(THD *thd, Item *a): Item_int_func(thd, a) {}
  Item_bool_func(THD *thd, Item *a, Item *b): Item_int_func(thd, a, b) {}
  Item_bool_func(THD *thd, Item *a, Item *b, Item *c): Item_int_func(thd, a, b, c) {}
  Item_bool_func(THD *thd, List<Item> &list): Item_int_func(thd, list) { }
  Item_bool_func(THD *thd, Item_bool_func *item) :Item_int_func(thd, item) {}
  bool is_bool_type() { return true; }
  virtual CHARSET_INFO *compare_collation() const { return NULL; }
  void fix_length_and_dec() { decimals=0; max_length=1; }
  uint decimal_precision() const { return 1; }
};


/**
  Abstract Item class, to represent <code>X IS [NOT] (TRUE | FALSE)</code>
  boolean predicates.
*/

class Item_func_truth : public Item_bool_func
{
public:
  virtual bool val_bool();
  virtual longlong val_int();
  virtual void fix_length_and_dec();
  virtual void print(String *str, enum_query_type query_type);

protected:
  Item_func_truth(THD *thd, Item *a, bool a_value, bool a_affirmative):
    Item_bool_func(thd, a), value(a_value), affirmative(a_affirmative)
  {}

  ~Item_func_truth()
  {}
private:
  /**
    True for <code>X IS [NOT] TRUE</code>,
    false for <code>X IS [NOT] FALSE</code> predicates.
  */
  const bool value;
  /**
    True for <code>X IS Y</code>, false for <code>X IS NOT Y</code> predicates.
  */
  const bool affirmative;
};


/**
  This Item represents a <code>X IS TRUE</code> boolean predicate.
*/

class Item_func_istrue : public Item_func_truth
{
public:
  Item_func_istrue(THD *thd, Item *a): Item_func_truth(thd, a, true, true) {}
  ~Item_func_istrue() {}
  virtual const char* func_name() const { return "istrue"; }
};


/**
  This Item represents a <code>X IS NOT TRUE</code> boolean predicate.
*/

class Item_func_isnottrue : public Item_func_truth
{
public:
  Item_func_isnottrue(THD *thd, Item *a):
    Item_func_truth(thd, a, true, false) {}
  ~Item_func_isnottrue() {}
  virtual const char* func_name() const { return "isnottrue"; }
};


/**
  This Item represents a <code>X IS FALSE</code> boolean predicate.
*/

class Item_func_isfalse : public Item_func_truth
{
public:
  Item_func_isfalse(THD *thd, Item *a): Item_func_truth(thd, a, false, true) {}
  ~Item_func_isfalse() {}
  virtual const char* func_name() const { return "isfalse"; }
};


/**
  This Item represents a <code>X IS NOT FALSE</code> boolean predicate.
*/

class Item_func_isnotfalse : public Item_func_truth
{
public:
  Item_func_isnotfalse(THD *thd, Item *a):
    Item_func_truth(thd, a, false, false) {}
  ~Item_func_isnotfalse() {}
  virtual const char* func_name() const { return "isnotfalse"; }
};


class Item_cache;
#define UNKNOWN (-1)


/*
  Item_in_optimizer(left_expr, Item_in_subselect(...))

  Item_in_optimizer is used to wrap an instance of Item_in_subselect. This
  class does the following:
   - Evaluate the left expression and store it in Item_cache_* object (to
     avoid re-evaluating it many times during subquery execution)
   - Shortcut the evaluation of "NULL IN (...)" to NULL in the cases where we
     don't care if the result is NULL or FALSE.

  NOTE
    It is not quite clear why the above listed functionality should be
    placed into a separate class called 'Item_in_optimizer'.
*/

class Item_in_optimizer: public Item_bool_func
{
protected:
  Item_cache *cache;
  Item *expr_cache;
  bool save_cache;
  /* 
    Stores the value of "NULL IN (SELECT ...)" for uncorrelated subqueries:
      UNKNOWN - "NULL in (SELECT ...)" has not yet been evaluated
      FALSE   - result is FALSE
      TRUE    - result is NULL
  */
  int result_for_null_param;
public:
  Item_in_optimizer(THD *thd, Item *a, Item *b):
    Item_bool_func(thd, a, b), cache(0), expr_cache(0),
    save_cache(0), result_for_null_param(UNKNOWN)
  { with_subselect= true; }
  bool fix_fields(THD *, Item **);
  bool fix_left(THD *thd);
  table_map not_null_tables() const { return 0; }
  bool is_null();
  longlong val_int();
  void cleanup();
  const char *func_name() const { return "<in_optimizer>"; }
  Item_cache **get_cache() { return &cache; }
  void keep_top_level_cache();
  Item *transform(THD *thd, Item_transformer transformer, uchar *arg);
  virtual Item *expr_cache_insert_transformer(THD *thd, uchar *unused);
  bool is_expensive_processor(uchar *arg);
  bool is_expensive();
  void set_join_tab_idx(uint join_tab_idx_arg)
  { args[1]->set_join_tab_idx(join_tab_idx_arg); }
  virtual void get_cache_parameters(List<Item> &parameters);
  bool is_top_level_item();
  bool eval_not_null_tables(uchar *opt_arg);
  void fix_after_pullout(st_select_lex *new_parent, Item **ref);
  bool invisible_mode();
  void reset_cache() { cache= NULL; }
};


/*
  Functions and operators with two arguments that can use range optimizer.
*/
class Item_bool_func2 :public Item_bool_func
{                                              /* Bool with 2 string args */
protected:
  void add_key_fields_optimize_op(JOIN *join, KEY_FIELD **key_fields,
                                  uint *and_level, table_map usable_tables,
                                  SARGABLE_PARAM **sargables, bool equal_func);
public:
  Item_bool_func2(THD *thd, Item *a, Item *b):
    Item_bool_func(thd, a, b) { }

  bool is_null() { return MY_TEST(args[0]->is_null() || args[1]->is_null()); }
  COND *remove_eq_conds(THD *thd, Item::cond_result *cond_value,
                        bool top_level);
  bool count_sargable_conds(uchar *arg);
  /*
    Specifies which result type the function uses to compare its arguments.
    This method is used in equal field propagation.
  */
  virtual Item_result compare_type() const
  {
    /*
      Have STRING_RESULT by default, which means the function compares
      val_str() results of the arguments. This is suitable for Item_func_like
      and for Item_func_spatial_rel.
      Note, Item_bool_rowready_func2 overrides this default behaviour.
    */
    return STRING_RESULT;
  }
  SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
  {
    DBUG_ENTER("Item_bool_func2::get_mm_tree");
    DBUG_ASSERT(arg_count == 2);
    SEL_TREE *ftree= get_full_func_mm_tree_for_args(param, args[0], args[1]);
    if (!ftree)
      ftree= Item_func::get_mm_tree(param, cond_ptr);
    DBUG_RETURN(ftree);
  }
};


/**
  A class for functions and operators that can use the range optimizer and
  have a reverse function/operator that can also use the range optimizer,
  so this condition:
    WHERE value OP field
  can be optimized as equivalent to:
    WHERE field REV_OP value

  This class covers:
  - scalar comparison predicates:  <, <=, =, <=>, >=, >
  - MBR and precise spatial relation predicates (e.g. SP_TOUCHES(x,y))

  For example:
    WHERE 10 > field
  can be optimized as:
    WHERE field < 10
*/
class Item_bool_func2_with_rev :public Item_bool_func2
{
protected:
  SEL_TREE *get_func_mm_tree(RANGE_OPT_PARAM *param,
                             Field *field, Item *value)
  {
    DBUG_ENTER("Item_bool_func2_with_rev::get_func_mm_tree");
    Item_func::Functype func_type=
      (value != arguments()[0]) ? functype() : rev_functype();
    DBUG_RETURN(get_mm_parts(param, field, func_type, value));
  }
public:
  Item_bool_func2_with_rev(THD *thd, Item *a, Item *b):
    Item_bool_func2(thd, a, b) { }
  virtual enum Functype rev_functype() const= 0;
  SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
  {
    DBUG_ENTER("Item_bool_func2_with_rev::get_mm_tree");
    DBUG_ASSERT(arg_count == 2);
    SEL_TREE *ftree;
    /*
      Even if get_full_func_mm_tree_for_args(param, args[0], args[1]) will not
      return a range predicate it may still be possible to create one
      by reversing the order of the operands. Note that this only
      applies to predicates where both operands are fields. Example: A
      query of the form

         WHERE t1.a OP t2.b

      In this case, args[0] == t1.a and args[1] == t2.b.
      When creating range predicates for t2,
      get_full_func_mm_tree_for_args(param, args[0], args[1])
      will return NULL because 'field' belongs to t1 and only
      predicates that applies to t2 are of interest. In this case a
      call to get_full_func_mm_tree_for_args() with reversed operands
      may succeed.
    */
    if (!(ftree= get_full_func_mm_tree_for_args(param, args[0], args[1])) &&
        !(ftree= get_full_func_mm_tree_for_args(param, args[1], args[0])))
      ftree= Item_func::get_mm_tree(param, cond_ptr);
    DBUG_RETURN(ftree);
  }
};


class Item_bool_rowready_func2 :public Item_bool_func2_with_rev
{
protected:
  Arg_comparator cmp;
public:
  Item_bool_rowready_func2(THD *thd, Item *a, Item *b):
    Item_bool_func2_with_rev(thd, a, b), cmp(tmp_arg, tmp_arg + 1)
  {
    allowed_arg_cols= 0;  // Fetch this value from first argument
  }
  void print(String *str, enum_query_type query_type)
  {
    Item_func::print_op(str, query_type);
  }
  Item *neg_transformer(THD *thd);
  virtual Item *negated_item(THD *thd);
  Item* propagate_equal_fields(THD *thd, const Context &ctx, COND_EQUAL *cond)
  {
    Item_args::propagate_equal_fields(thd,
                                      Context(ANY_SUBST,
                                              cmp.compare_type(),
                                              compare_collation()),
                                      cond);
    return this;
  }
  void fix_length_and_dec();
  int set_cmp_func()
  {
    return cmp.set_cmp_func(this, tmp_arg, tmp_arg + 1, true);
  }
  CHARSET_INFO *compare_collation() const { return cmp.compare_collation(); }
  Item_result compare_type() const { return cmp.compare_type(); }
  Arg_comparator *get_comparator() { return &cmp; }
  void cleanup()
  {
    Item_bool_func2::cleanup();
    cmp.cleanup();
  }
  void add_key_fields(JOIN *join, KEY_FIELD **key_fields,
                      uint *and_level, table_map usable_tables,
                      SARGABLE_PARAM **sargables)
  {
    return add_key_fields_optimize_op(join, key_fields, and_level,
                                      usable_tables, sargables, false);
  }
};

/**
  XOR inherits from Item_bool_func because it is not optimized yet.
  Later, when XOR is optimized, it needs to inherit from
  Item_cond instead. See WL#5800. 
*/
class Item_func_xor :public Item_bool_func
{
public:
  Item_func_xor(THD *thd, Item *i1, Item *i2): Item_bool_func(thd, i1, i2) {}
  enum Functype functype() const { return XOR_FUNC; }
  const char *func_name() const { return "xor"; }
  void print(String *str, enum_query_type query_type)
  { Item_func::print_op(str, query_type); }
  longlong val_int();
  Item *neg_transformer(THD *thd);
  Item* propagate_equal_fields(THD *thd, const Context &ctx, COND_EQUAL *cond)
  {
    Item_args::propagate_equal_fields(thd, Context_boolean(), cond);
    return this;
  }
};

class Item_func_not :public Item_bool_func
{
  bool abort_on_null;
public:
  Item_func_not(THD *thd, Item *a):
    Item_bool_func(thd, a), abort_on_null(FALSE) {}
  virtual void top_level_item() { abort_on_null= 1; }
  bool is_top_level_item() { return abort_on_null; }
  longlong val_int();
  enum Functype functype() const { return NOT_FUNC; }
  const char *func_name() const { return "not"; }
  Item *neg_transformer(THD *thd);
  bool fix_fields(THD *, Item **);
  virtual void print(String *str, enum_query_type query_type);
};

class Item_maxmin_subselect;

/*
  trigcond<param>(arg) ::= param? arg : TRUE

  The class Item_func_trig_cond is used for guarded predicates 
  which are employed only for internal purposes.
  A guarded predicate is an object consisting of an a regular or
  a guarded predicate P and a pointer to a boolean guard variable g. 
  A guarded predicate P/g is evaluated to true if the value of the
  guard g is false, otherwise it is evaluated to the same value that
  the predicate P: val(P/g)= g ? val(P):true.
  Guarded predicates allow us to include predicates into a conjunction
  conditionally. Currently they are utilized for pushed down predicates
  in queries with outer join operations.

  In the future, probably, it makes sense to extend this class to
  the objects consisting of three elements: a predicate P, a pointer
  to a variable g and a firing value s with following evaluation
  rule: val(P/g,s)= g==s? val(P) : true. It will allow us to build only
  one item for the objects of the form P/g1/g2... 

  Objects of this class are built only for query execution after
  the execution plan has been already selected. That's why this
  class needs only val_int out of generic methods. 
 
  Current uses of Item_func_trig_cond objects:
   - To wrap selection conditions when executing outer joins
   - To wrap condition that is pushed down into subquery
*/

class Item_func_trig_cond: public Item_bool_func
{
  bool *trig_var;
public:
  Item_func_trig_cond(THD *thd, Item *a, bool *f): Item_bool_func(thd, a)
  { trig_var= f; }
  longlong val_int() { return *trig_var ? args[0]->val_int() : 1; }
  enum Functype functype() const { return TRIG_COND_FUNC; };
  const char *func_name() const { return "trigcond"; };
  bool const_item() const { return FALSE; }
  bool *get_trig_var() { return trig_var; }
  void add_key_fields(JOIN *join, KEY_FIELD **key_fields,
                      uint *and_level, table_map usable_tables,
                      SARGABLE_PARAM **sargables);
};

class Item_func_not_all :public Item_func_not
{
  /* allow to check presence of values in max/min optimization */
  Item_sum_hybrid *test_sum_item;
  Item_maxmin_subselect *test_sub_item;

public:
  bool show;

  Item_func_not_all(THD *thd, Item *a):
    Item_func_not(thd, a), test_sum_item(0), test_sub_item(0), show(0)
    {}
  table_map not_null_tables() const { return 0; }
  longlong val_int();
  enum Functype functype() const { return NOT_ALL_FUNC; }
  const char *func_name() const { return "<not>"; }
  bool fix_fields(THD *thd, Item **ref)
    {return Item_func::fix_fields(thd, ref);}
  virtual void print(String *str, enum_query_type query_type);
  void set_sum_test(Item_sum_hybrid *item) { test_sum_item= item; test_sub_item= 0; };
  void set_sub_test(Item_maxmin_subselect *item) { test_sub_item= item; test_sum_item= 0;};
  bool empty_underlying_subquery();
  Item *neg_transformer(THD *thd);
};


class Item_func_nop_all :public Item_func_not_all
{
public:

  Item_func_nop_all(THD *thd, Item *a): Item_func_not_all(thd, a) {}
  longlong val_int();
  const char *func_name() const { return "<nop>"; }
  Item *neg_transformer(THD *thd);
};


class Item_func_eq :public Item_bool_rowready_func2
{
  bool abort_on_null;
public:
  Item_func_eq(THD *thd, Item *a, Item *b):
    Item_bool_rowready_func2(thd, a, b),
    abort_on_null(false), in_equality_no(UINT_MAX)
  {}
  longlong val_int();
  enum Functype functype() const { return EQ_FUNC; }
  enum Functype rev_functype() const { return EQ_FUNC; }
  cond_result eq_cmp_result() const { return COND_TRUE; }
  const char *func_name() const { return "="; }
  void top_level_item() { abort_on_null= true; }
  Item *negated_item(THD *thd);
  COND *build_equal_items(THD *thd, COND_EQUAL *inherited,
                          bool link_item_fields,
                          COND_EQUAL **cond_equal_ref);
  void add_key_fields(JOIN *join, KEY_FIELD **key_fields,
                      uint *and_level, table_map usable_tables,
                      SARGABLE_PARAM **sargables)
  {
    return add_key_fields_optimize_op(join, key_fields, and_level,
                                      usable_tables, sargables, true);
  }
  bool check_equality(THD *thd, COND_EQUAL *cond, List<Item> *eq_list);
  /* 
    - If this equality is created from the subquery's IN-equality:
      number of the item it was created from, e.g. for
       (a,b) IN (SELECT c,d ...)  a=c will have in_equality_no=0, 
       and b=d will have in_equality_no=1.
    - Otherwise, UINT_MAX
  */
  uint in_equality_no;
  virtual uint exists2in_reserved_items() { return 1; };
  friend class  Arg_comparator;
};

class Item_func_equal :public Item_bool_rowready_func2
{
public:
  Item_func_equal(THD *thd, Item *a, Item *b):
    Item_bool_rowready_func2(thd, a, b) {}
  longlong val_int();
  void fix_length_and_dec();
  table_map not_null_tables() const { return 0; }
  enum Functype functype() const { return EQUAL_FUNC; }
  enum Functype rev_functype() const { return EQUAL_FUNC; }
  cond_result eq_cmp_result() const { return COND_TRUE; }
  const char *func_name() const { return "<=>"; }
  Item *neg_transformer(THD *thd) { return 0; }
  void add_key_fields(JOIN *join, KEY_FIELD **key_fields,
                      uint *and_level, table_map usable_tables,
                      SARGABLE_PARAM **sargables)
  {
    return add_key_fields_optimize_op(join, key_fields, and_level,
                                      usable_tables, sargables, true);
  }
};


class Item_func_ge :public Item_bool_rowready_func2
{
public:
  Item_func_ge(THD *thd, Item *a, Item *b):
    Item_bool_rowready_func2(thd, a, b) {};
  longlong val_int();
  enum Functype functype() const { return GE_FUNC; }
  enum Functype rev_functype() const { return LE_FUNC; }
  cond_result eq_cmp_result() const { return COND_TRUE; }
  const char *func_name() const { return ">="; }
  Item *negated_item(THD *thd);
};


class Item_func_gt :public Item_bool_rowready_func2
{
public:
  Item_func_gt(THD *thd, Item *a, Item *b):
    Item_bool_rowready_func2(thd, a, b) {};
  longlong val_int();
  enum Functype functype() const { return GT_FUNC; }
  enum Functype rev_functype() const { return LT_FUNC; }
  cond_result eq_cmp_result() const { return COND_FALSE; }
  const char *func_name() const { return ">"; }
  Item *negated_item(THD *thd);
};


class Item_func_le :public Item_bool_rowready_func2
{
public:
  Item_func_le(THD *thd, Item *a, Item *b):
    Item_bool_rowready_func2(thd, a, b) {};
  longlong val_int();
  enum Functype functype() const { return LE_FUNC; }
  enum Functype rev_functype() const { return GE_FUNC; }
  cond_result eq_cmp_result() const { return COND_TRUE; }
  const char *func_name() const { return "<="; }
  Item *negated_item(THD *thd);
};


class Item_func_lt :public Item_bool_rowready_func2
{
public:
  Item_func_lt(THD *thd, Item *a, Item *b):
    Item_bool_rowready_func2(thd, a, b) {}
  longlong val_int();
  enum Functype functype() const { return LT_FUNC; }
  enum Functype rev_functype() const { return GT_FUNC; }
  cond_result eq_cmp_result() const { return COND_FALSE; }
  const char *func_name() const { return "<"; }
  Item *negated_item(THD *thd);
};


class Item_func_ne :public Item_bool_rowready_func2
{
protected:
  SEL_TREE *get_func_mm_tree(RANGE_OPT_PARAM *param,
                             Field *field, Item *value)
  {
    DBUG_ENTER("Item_func_ne::get_func_mm_tree");
    DBUG_RETURN(get_ne_mm_tree(param, field, value, value));
  }
public:
  Item_func_ne(THD *thd, Item *a, Item *b):
    Item_bool_rowready_func2(thd, a, b) {}
  longlong val_int();
  enum Functype functype() const { return NE_FUNC; }
  enum Functype rev_functype() const { return NE_FUNC; }
  cond_result eq_cmp_result() const { return COND_FALSE; }
  const char *func_name() const { return "<>"; }
  Item *negated_item(THD *thd);
  void add_key_fields(JOIN *join, KEY_FIELD **key_fields, uint *and_level,
                      table_map usable_tables, SARGABLE_PARAM **sargables);
};


/*
  The class Item_func_opt_neg is defined to factor out the functionality
  common for the classes Item_func_between and Item_func_in. The objects
  of these classes can express predicates or there negations.
  The alternative approach would be to create pairs Item_func_between,
  Item_func_notbetween and Item_func_in, Item_func_notin.

*/

class Item_func_opt_neg :public Item_bool_func
{
protected:
  /*
    The result type that will be used for comparison.
    cmp_type() of all arguments are collected to here.
  */
  Item_result m_compare_type;
  /*
    The collation that will be used for comparison in case
    when m_compare_type is STRING_RESULT.
  */
  DTCollation cmp_collation;
public:
  bool negated;     /* <=> the item represents NOT <func> */
  bool pred_level;  /* <=> [NOT] <func> is used on a predicate level */
public:
  Item_func_opt_neg(THD *thd, Item *a, Item *b, Item *c):
    Item_bool_func(thd, a, b, c), negated(0), pred_level(0) {}
  Item_func_opt_neg(THD *thd, List<Item> &list):
    Item_bool_func(thd, list), negated(0), pred_level(0) {}
public:
  inline void negate() { negated= !negated; }
  inline void top_level_item() { pred_level= 1; }
  bool is_top_level_item() const { return pred_level; }
  Item *neg_transformer(THD *thd)
  {
    negated= !negated;
    return this;
  }
  bool eq(const Item *item, bool binary_cmp) const;
  CHARSET_INFO *compare_collation() const { return cmp_collation.collation; }
  Item* propagate_equal_fields(THD *, const Context &, COND_EQUAL *) = 0;
};


class Item_func_between :public Item_func_opt_neg
{
protected:
  SEL_TREE *get_func_mm_tree(RANGE_OPT_PARAM *param,
                             Field *field, Item *value);
public:
  String value0,value1,value2;
  /* TRUE <=> arguments will be compared as dates. */
  Item *compare_as_dates;
  Item_func_between(THD *thd, Item *a, Item *b, Item *c):
    Item_func_opt_neg(thd, a, b, c), compare_as_dates(FALSE) { }
  longlong val_int();
  enum Functype functype() const   { return BETWEEN; }
  const char *func_name() const { return "between"; }
  void fix_length_and_dec();
  virtual void print(String *str, enum_query_type query_type);
  bool eval_not_null_tables(uchar *opt_arg);
  void fix_after_pullout(st_select_lex *new_parent, Item **ref);
  bool count_sargable_conds(uchar *arg);
  void add_key_fields(JOIN *join, KEY_FIELD **key_fields,
                      uint *and_level, table_map usable_tables,
                      SARGABLE_PARAM **sargables);
  SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr);
  Item* propagate_equal_fields(THD *thd, const Context &ctx, COND_EQUAL *cond)
  {
    Item_args::propagate_equal_fields(thd,
                                      Context(ANY_SUBST,
                                              m_compare_type,
                                              compare_collation()),
                                      cond);
    return this;
  }
};


class Item_func_strcmp :public Item_int_func
{
  String value1, value2;
  DTCollation cmp_collation;
public:
  Item_func_strcmp(THD *thd, Item *a, Item *b):
    Item_int_func(thd, a, b) {}
  longlong val_int();
  uint decimal_precision() const { return 1; }
  const char *func_name() const { return "strcmp"; }
  void fix_length_and_dec()
  {
    agg_arg_charsets_for_comparison(cmp_collation, args, 2);
    fix_char_length(2); // returns "1" or "0" or "-1"
  }
};


struct interval_range
{
  Item_result type;
  double dbl;
  my_decimal dec;
};

class Item_func_interval :public Item_int_func
{
  Item_row *row;
  bool use_decimal_comparison;
  interval_range *intervals;
public:
  Item_func_interval(THD *thd, Item_row *a):
    Item_int_func(thd, a), row(a), intervals(0)
  {
    allowed_arg_cols= 0;    // Fetch this value from first argument
  }
  longlong val_int();
  void fix_length_and_dec();
  const char *func_name() const { return "interval"; }
  uint decimal_precision() const { return 2; }
  void print(String *str, enum_query_type query_type)
  {
    str->append(func_name());
    print_args(str, 0, query_type);
  }
};


class Item_func_coalesce :public Item_func_hybrid_field_type
{
public:
  Item_func_coalesce(THD *thd, Item *a, Item *b):
    Item_func_hybrid_field_type(thd, a, b) {}
  Item_func_coalesce(THD *thd, List<Item> &list):
    Item_func_hybrid_field_type(thd, list) {}
  double real_op();
  longlong int_op();
  String *str_op(String *);
  my_decimal *decimal_op(my_decimal *);
  bool date_op(MYSQL_TIME *ltime,uint fuzzydate);
  void fix_length_and_dec()
  {
    set_handler_by_field_type(agg_field_type(args, arg_count, true));
    fix_attributes(args, arg_count);
  }
  const char *func_name() const { return "coalesce"; }
  table_map not_null_tables() const { return 0; }
};


/*
  Case abbreviations that aggregate its result field type by two arguments:
    IFNULL(arg1, arg2)
    IF(switch, arg1, arg2)
*/
class Item_func_case_abbreviation2 :public Item_func_hybrid_field_type
{
protected:
  void fix_length_and_dec2(Item **items)
  {
    set_handler_by_field_type(agg_field_type(items, 2, true));
    fix_attributes(items, 2);
  }
  uint decimal_precision2(Item **args) const;
public:
  Item_func_case_abbreviation2(THD *thd, Item *a, Item *b):
    Item_func_hybrid_field_type(thd, a, b) { }
  Item_func_case_abbreviation2(THD *thd, Item *a, Item *b, Item *c):
    Item_func_hybrid_field_type(thd, a, b, c) { }
};


class Item_func_ifnull :public Item_func_case_abbreviation2
{
public:
  Item_func_ifnull(THD *thd, Item *a, Item *b):
    Item_func_case_abbreviation2(thd, a, b) {}
  double real_op();
  longlong int_op();
  String *str_op(String *str);
  my_decimal *decimal_op(my_decimal *);
  bool date_op(MYSQL_TIME *ltime,uint fuzzydate);
  void fix_length_and_dec()
  {
    Item_func_case_abbreviation2::fix_length_and_dec2(args);
    maybe_null= args[1]->maybe_null;
  }
  const char *func_name() const { return "ifnull"; }
  Field *create_field_for_create_select(TABLE *table)
  { return tmp_table_field_from_field_type(table, false, false); }

  table_map not_null_tables() const { return 0; }
  uint decimal_precision() const
  {
    return Item_func_case_abbreviation2::decimal_precision2(args);
  }
};


class Item_func_if :public Item_func_case_abbreviation2
{
public:
  Item_func_if(THD *thd, Item *a, Item *b, Item *c):
    Item_func_case_abbreviation2(thd, a, b, c)
  {}
  bool date_op(MYSQL_TIME *ltime, uint fuzzydate);
  longlong int_op();
  double real_op();
  my_decimal *decimal_op(my_decimal *);
  String *str_op(String *);
  bool fix_fields(THD *, Item **);
  void fix_length_and_dec();
  uint decimal_precision() const
  {
    return Item_func_case_abbreviation2::decimal_precision2(args + 1);
  }
  const char *func_name() const { return "if"; }
  bool eval_not_null_tables(uchar *opt_arg);
  void fix_after_pullout(st_select_lex *new_parent, Item **ref);
private:
  void cache_type_info(Item *source);
};


class Item_func_nullif :public Item_func_hybrid_field_type
{
  Arg_comparator cmp;
  /*
    NULLIF(a,b) is a short for:
      CASE WHEN a=b THEN NULL ELSE a END

    The left "a" is for comparison purposes.
    The right "a" is for return value purposes.
    These are two different "a" and they can be replaced to different items.

    The left "a" is in a comparison and can be replaced by:
    - Item_func::convert_const_compared_to_int_field()
    - agg_item_set_converter() in set_cmp_func()
    - Arg_comparator::cache_converted_constant() in set_cmp_func()

    Both "a"s are subject to equal fields propagation and can be replaced by:
    - Item_field::propagate_equal_fields(ANY_SUBST) for the left "a"
    - Item_field::propagate_equal_fields(IDENTITY_SUBST) for the right "a"
  */
  Item_cache *m_cache;
  int compare();
public:
  /*
    Here we pass three arguments to the parent constructor, as NULLIF
    is a three-argument function, it needs two copies of the first argument
    (see above). But fix_fields() will be confused if we try to prepare the
    same Item twice (if args[0]==args[2]), so we hide the third argument
    (decrementing arg_count) and copy args[2]=args[0] again after fix_fields().
    See also Item_func_nullif::fix_length_and_dec().
  */
  Item_func_nullif(THD *thd, Item *a, Item *b):
    Item_func_hybrid_field_type(thd, a, b, a),
    m_cache(NULL)
  { arg_count--; }
  bool date_op(MYSQL_TIME *ltime, uint fuzzydate);
  double real_op();
  longlong int_op();
  String *str_op(String *str);
  my_decimal *decimal_op(my_decimal *);
  void fix_length_and_dec();
  bool walk(Item_processor processor, bool walk_subquery, uchar *arg);
  uint decimal_precision() const { return args[2]->decimal_precision(); }
  const char *func_name() const { return "nullif"; }
  void print(String *str, enum_query_type query_type);
  void split_sum_func(THD *thd, Item **ref_pointer_array, List<Item> &fields,
                      uint flags);
  void update_used_tables();
  table_map not_null_tables() const { return 0; }
  bool is_null();
  Item* propagate_equal_fields(THD *thd, const Context &ctx, COND_EQUAL *cond)
  {
    Context cmpctx(ANY_SUBST, cmp.compare_type(), cmp.compare_collation());
    const Item *old0= args[0];
    args[0]->propagate_equal_fields_and_change_item_tree(thd, cmpctx,
                                                         cond, &args[0]);
    args[1]->propagate_equal_fields_and_change_item_tree(thd, cmpctx,
                                                         cond, &args[1]);
    /*
      MDEV-9712 Performance degradation of nested NULLIF
      ANY_SUBST is more relaxed than IDENTITY_SUBST.
      If ANY_SUBST did not change args[0],
      then we can skip propagation for args[2].
    */
    if (old0 != args[0])
      args[2]->propagate_equal_fields_and_change_item_tree(thd,
                                                           Context_identity(),
                                                           cond, &args[2]);
    return this;
  }
};


/* Functions to handle the optimized IN */


/* A vector of values of some type  */

class in_vector :public Sql_alloc
{
public:
  char *base;
  uint size;
  qsort2_cmp compare;
  CHARSET_INFO *collation;
  uint count;
  uint used_count;
  in_vector() {}
  in_vector(uint elements,uint element_length,qsort2_cmp cmp_func, 
  	    CHARSET_INFO *cmp_coll)
    :base((char*) sql_calloc(elements*element_length)),
     size(element_length), compare(cmp_func), collation(cmp_coll),
     count(elements), used_count(elements) {}
  virtual ~in_vector() {}
  virtual void set(uint pos,Item *item)=0;
  virtual uchar *get_value(Item *item)=0;
  void sort()
  {
    my_qsort2(base,used_count,size,compare,(void*)collation);
  }
  bool find(Item *item);
  
  /* 
    Create an instance of Item_{type} (e.g. Item_decimal) constant object
    which type allows it to hold an element of this vector without any
    conversions.
    The purpose of this function is to be able to get elements of this
    vector in form of Item_xxx constants without creating Item_xxx object
    for every array element you get (i.e. this implements "FlyWeight" pattern)
  */
  virtual Item* create_item(THD *thd) { return NULL; }
  
  /*
    Store the value at position #pos into provided item object
    SYNOPSIS
      value_to_item()
        pos   Index of value to store
        item  Constant item to store value into. The item must be of the same
              type that create_item() returns.
  */
  virtual void value_to_item(uint pos, Item *item) { }
  
  /* Compare values number pos1 and pos2 for equality */
  bool compare_elems(uint pos1, uint pos2)
  {
    return MY_TEST(compare(collation, base + pos1 * size, base + pos2 * size));
  }
  virtual Item_result result_type()= 0;
};

class in_string :public in_vector
{
  char buff[STRING_BUFFER_USUAL_SIZE];
  String tmp;
  class Item_string_for_in_vector: public Item_string
  {
  public:
    Item_string_for_in_vector(THD *thd, CHARSET_INFO *cs):
      Item_string(thd, cs)
    { }
    void set_value(const String *str)
    {
      str_value= *str;
      collation.set(str->charset());
    }
  };
public:
  in_string(uint elements,qsort2_cmp cmp_func, CHARSET_INFO *cs);
  ~in_string();
  void set(uint pos,Item *item);
  uchar *get_value(Item *item);
  Item* create_item(THD *thd);
  void value_to_item(uint pos, Item *item)
  {    
    String *str=((String*) base)+pos;
    Item_string_for_in_vector *to= (Item_string_for_in_vector*) item;
    to->set_value(str);
  }
  Item_result result_type() { return STRING_RESULT; }
};

class in_longlong :public in_vector
{
protected:
  /*
    Here we declare a temporary variable (tmp) of the same type as the
    elements of this vector. tmp is used in finding if a given value is in 
    the list. 
  */
  struct packed_longlong 
  {
    longlong val;
    longlong unsigned_flag;  // Use longlong, not bool, to preserve alignment
  } tmp;
public:
  in_longlong(uint elements);
  void set(uint pos,Item *item);
  uchar *get_value(Item *item);
  Item* create_item(THD *thd);
  void value_to_item(uint pos, Item *item)
  {
    ((Item_int*) item)->value= ((packed_longlong*) base)[pos].val;
    ((Item_int*) item)->unsigned_flag= (bool)
      ((packed_longlong*) base)[pos].unsigned_flag;
  }
  Item_result result_type() { return INT_RESULT; }

  friend int cmp_longlong(void *cmp_arg, packed_longlong *a,packed_longlong *b);
};


/*
  Class to represent a vector of constant DATE/DATETIME values.
  Values are obtained with help of the get_datetime_value() function.
  If the left item is a constant one then its value is cached in the
  lval_cache variable.
*/
class in_datetime :public in_longlong
{
public:
  THD *thd;
  /* An item used to issue warnings. */
  Item *warn_item;
  /* Cache for the left item. */
  Item *lval_cache;

  in_datetime(Item *warn_item_arg, uint elements)
    :in_longlong(elements), thd(current_thd), warn_item(warn_item_arg),
     lval_cache(0) {};
  void set(uint pos,Item *item);
  uchar *get_value(Item *item);
  Item *create_item(THD *thd);
  void value_to_item(uint pos, Item *item)
  {
    packed_longlong *val= reinterpret_cast<packed_longlong*>(base)+pos;
    Item_datetime *dt= reinterpret_cast<Item_datetime*>(item);
    dt->set(val->val);
  }
  friend int cmp_longlong(void *cmp_arg, packed_longlong *a,packed_longlong *b);
};


class in_double :public in_vector
{
  double tmp;
public:
  in_double(uint elements);
  void set(uint pos,Item *item);
  uchar *get_value(Item *item);
  Item *create_item(THD *thd);
  void value_to_item(uint pos, Item *item)
  {
    ((Item_float*)item)->value= ((double*) base)[pos];
  }
  Item_result result_type() { return REAL_RESULT; }
};


class in_decimal :public in_vector
{
  my_decimal val;
public:
  in_decimal(uint elements);
  void set(uint pos, Item *item);
  uchar *get_value(Item *item);
  Item *create_item(THD *thd);
  void value_to_item(uint pos, Item *item)
  {
    my_decimal *dec= ((my_decimal *)base) + pos;
    Item_decimal *item_dec= (Item_decimal*)item;
    item_dec->set_decimal_value(dec);
  }
  Item_result result_type() { return DECIMAL_RESULT; }

};


/*
** Classes for easy comparing of non const items
*/

class cmp_item :public Sql_alloc
{
public:
  CHARSET_INFO *cmp_charset;
  cmp_item() { cmp_charset= &my_charset_bin; }
  virtual ~cmp_item() {}
  virtual void store_value(Item *item)= 0;
  /**
     @returns result (TRUE, FALSE or UNKNOWN) of
     "stored argument's value <> item's value"
  */
  virtual int cmp(Item *item)= 0;
  // for optimized IN with row
  virtual int compare(cmp_item *item)= 0;
  static cmp_item* get_comparator(Item_result type, Item * warn_item,
                                  CHARSET_INFO *cs);
  virtual cmp_item *make_same()= 0;
  virtual void store_value_by_template(THD *thd, cmp_item *tmpl, Item *item)
  {
    store_value(item);
  }
};

/// cmp_item which stores a scalar (i.e. non-ROW).
class cmp_item_scalar : public cmp_item
{
protected:
  bool m_null_value;                            ///< If stored value is NULL
};

class cmp_item_string : public cmp_item_scalar
{
protected:
  String *value_res;
public:
  cmp_item_string () {}
  cmp_item_string (CHARSET_INFO *cs) { cmp_charset= cs; }
  void set_charset(CHARSET_INFO *cs) { cmp_charset= cs; }
  friend class cmp_item_sort_string;
  friend class cmp_item_sort_string_in_static;
};

class cmp_item_sort_string :public cmp_item_string
{
protected:
  char value_buff[STRING_BUFFER_USUAL_SIZE];
  String value;
public:
  cmp_item_sort_string():
    cmp_item_string() {}
  cmp_item_sort_string(CHARSET_INFO *cs):
    cmp_item_string(cs),
    value(value_buff, sizeof(value_buff), cs) {}
  void store_value(Item *item)
  {
    value_res= item->val_str(&value);
    m_null_value= item->null_value;
  }
  int cmp(Item *arg)
  {
    char buff[STRING_BUFFER_USUAL_SIZE];
    String tmp(buff, sizeof(buff), cmp_charset), *res= arg->val_str(&tmp);
    if (m_null_value || arg->null_value)
      return UNKNOWN;
    if (value_res && res)
      return sortcmp(value_res, res, cmp_charset) != 0;
    else if (!value_res && !res)
      return FALSE;
    else
      return TRUE;
  }
  int compare(cmp_item *ci)
  {
    cmp_item_string *l_cmp= (cmp_item_string *) ci;
    return sortcmp(value_res, l_cmp->value_res, cmp_charset);
  } 
  cmp_item *make_same();
  void set_charset(CHARSET_INFO *cs)
  {
    cmp_charset= cs;
    value.set_quick(value_buff, sizeof(value_buff), cs);
  }
};

class cmp_item_int : public cmp_item_scalar
{
  longlong value;
public:
  cmp_item_int() {}                           /* Remove gcc warning */
  void store_value(Item *item)
  {
    value= item->val_int();
    m_null_value= item->null_value;
  }
  int cmp(Item *arg)
  {
    const bool rc= value != arg->val_int();
    return (m_null_value || arg->null_value) ? UNKNOWN : rc;
  }
  int compare(cmp_item *ci)
  {
    cmp_item_int *l_cmp= (cmp_item_int *)ci;
    return (value < l_cmp->value) ? -1 : ((value == l_cmp->value) ? 0 : 1);
  }
  cmp_item *make_same();
};

/*
  Compare items in the DATETIME context.
  Values are obtained with help of the get_datetime_value() function.
  If the left item is a constant one then its value is cached in the
  lval_cache variable.
*/
class cmp_item_datetime : public cmp_item_scalar
{
  longlong value;
public:
  THD *thd;
  /* Item used for issuing warnings. */
  Item *warn_item;
  /* Cache for the left item. */
  Item *lval_cache;

  cmp_item_datetime(Item *warn_item_arg)
    :thd(current_thd), warn_item(warn_item_arg), lval_cache(0) {}
  void store_value(Item *item);
  int cmp(Item *arg);
  int compare(cmp_item *ci);
  cmp_item *make_same();
};

class cmp_item_real : public cmp_item_scalar
{
  double value;
public:
  cmp_item_real() {}                          /* Remove gcc warning */
  void store_value(Item *item)
  {
    value= item->val_real();
    m_null_value= item->null_value;
  }
  int cmp(Item *arg)
  {
    const bool rc= value != arg->val_real();
    return (m_null_value || arg->null_value) ? UNKNOWN : rc;
  }
  int compare(cmp_item *ci)
  {
    cmp_item_real *l_cmp= (cmp_item_real *) ci;
    return (value < l_cmp->value)? -1 : ((value == l_cmp->value) ? 0 : 1);
  }
  cmp_item *make_same();
};


class cmp_item_decimal : public cmp_item_scalar
{
  my_decimal value;
public:
  cmp_item_decimal() {}                       /* Remove gcc warning */
  void store_value(Item *item);
  int cmp(Item *arg);
  int compare(cmp_item *c);
  cmp_item *make_same();
};


/* 
   cmp_item for optimized IN with row (right part string, which never
   be changed)
*/

class cmp_item_sort_string_in_static :public cmp_item_string
{
 protected:
  String value;
public:
  cmp_item_sort_string_in_static(CHARSET_INFO *cs):
    cmp_item_string(cs) {}
  void store_value(Item *item)
  {
    value_res= item->val_str(&value);
    m_null_value= item->null_value;
  }
  int cmp(Item *item)
  {
    // Should never be called
    DBUG_ASSERT(false);
    return TRUE;
  }
  int compare(cmp_item *ci)
  {
    cmp_item_string *l_cmp= (cmp_item_string *) ci;
    return sortcmp(value_res, l_cmp->value_res, cmp_charset);
  }
  cmp_item *make_same()
  {
    return new cmp_item_sort_string_in_static(cmp_charset);
  }
};


/*
  The class Item_func_case is the CASE ... WHEN ... THEN ... END function
  implementation.

  When there is no expression between CASE and the first WHEN 
  (the CASE expression) then this function simple checks all WHEN expressions
  one after another. When some WHEN expression evaluated to TRUE then the
  value of the corresponding THEN expression is returned.

  When the CASE expression is specified then it is compared to each WHEN
  expression individually. When an equal WHEN expression is found
  corresponding THEN expression is returned.
  In order to do correct comparisons several comparators are used. One for
  each result type. Different result types that are used in particular
  CASE ... END expression are collected in the fix_length_and_dec() member
  function and only comparators for there result types are used.
*/

class Item_func_case :public Item_func_hybrid_field_type
{
  int first_expr_num, else_expr_num;
  enum Item_result left_cmp_type;
  String tmp_value;
  uint ncases;
  Item_result cmp_type;
  DTCollation cmp_collation;
  cmp_item *cmp_items[6]; /* For all result types */
  cmp_item *case_item;
  Item **arg_buffer;
  uint m_found_types;
public:
  Item_func_case(THD *thd, List<Item> &list, Item *first_expr_arg,
                 Item *else_expr_arg);
  double real_op();
  longlong int_op();
  String *str_op(String *);
  my_decimal *decimal_op(my_decimal *);
  bool date_op(MYSQL_TIME *ltime, uint fuzzydate);
  bool fix_fields(THD *thd, Item **ref);
  void fix_length_and_dec();
  uint decimal_precision() const;
  table_map not_null_tables() const { return 0; }
  const char *func_name() const { return "case"; }
  virtual void print(String *str, enum_query_type query_type);
  Item *find_item(String *str);
  CHARSET_INFO *compare_collation() const { return cmp_collation.collation; }
  void cleanup();
  Item* propagate_equal_fields(THD *thd, const Context &ctx, COND_EQUAL *cond);
};

/*
  The Item_func_in class implements
  in_expr IN (<in value list>)
  and
  in_expr NOT IN (<in value list>)

  The current implementation distinguishes 2 cases:
  1) all items in <in value list> are constants and have the same
    result type. This case is handled by in_vector class.
  2) otherwise Item_func_in employs several cmp_item objects to perform
    comparisons of in_expr and an item from <in value list>. One cmp_item
    object for each result type. Different result types are collected in the
    fix_length_and_dec() member function by means of collect_cmp_types()
    function.
*/
class Item_func_in :public Item_func_opt_neg
{
  /**
     Usable if <in value list> is made only of constants. Returns true if one
     of these constants contains a NULL. Example:
     IN ( (-5, (12,NULL)), ... ).
  */
  bool list_contains_null();
protected:
  SEL_TREE *get_func_mm_tree(RANGE_OPT_PARAM *param,
                             Field *field, Item *value);
public:
  /// An array of values, created when the bisection lookup method is used
  in_vector *array;
  /**
    If there is some NULL among <in value list>, during a val_int() call; for
    example
    IN ( (1,(3,'col')), ... ), where 'col' is a column which evaluates to
    NULL.
  */
  bool have_null;
  /**
    true when all arguments of the IN list are of compatible types
    and can be used safely as comparisons for key conditions
  */
  bool arg_types_compatible;
  Item_result left_cmp_type;
  cmp_item *cmp_items[6]; /* One cmp_item for each result type */

  Item_func_in(THD *thd, List<Item> &list):
    Item_func_opt_neg(thd, list), array(0), have_null(0),
    arg_types_compatible(FALSE)
  {
    bzero(&cmp_items, sizeof(cmp_items));
    allowed_arg_cols= 0;  // Fetch this value from first argument
  }
  longlong val_int();
  bool fix_fields(THD *, Item **);
  void fix_length_and_dec();
  void cleanup()
  {
    uint i;
    DBUG_ENTER("Item_func_in::cleanup");
    Item_int_func::cleanup();
    delete array;
    array= 0;
    for (i= 0; i <= (uint)TIME_RESULT; i++)
    {
      delete cmp_items[i];
      cmp_items[i]= 0;
    }
    DBUG_VOID_RETURN;
  }
  void add_key_fields(JOIN *join, KEY_FIELD **key_fields, uint *and_level,
                      table_map usable_tables, SARGABLE_PARAM **sargables);
  SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr);
  Item* propagate_equal_fields(THD *thd, const Context &ctx, COND_EQUAL *cond)
  {
    /*
      Note, we pass ANY_SUBST, this makes sure that non of the args
      will be replaced to a zero-filled Item_string.
      Such a change would require rebuilding of cmp_items.
    */
    Context cmpctx(ANY_SUBST, m_compare_type,
                   Item_func_in::compare_collation());
    for (uint i= 0; i < arg_count; i++)
    {
      if (arg_types_compatible || i > 0)
        args[i]->propagate_equal_fields_and_change_item_tree(thd, cmpctx,
                                                             cond, &args[i]);
    }
    return this;
  }
  virtual void print(String *str, enum_query_type query_type);
  enum Functype functype() const { return IN_FUNC; }
  const char *func_name() const { return " IN "; }
  bool eval_not_null_tables(uchar *opt_arg);
  void fix_after_pullout(st_select_lex *new_parent, Item **ref);
  bool count_sargable_conds(uchar *arg);
};

class cmp_item_row :public cmp_item
{
  cmp_item **comparators;
  uint n;
public:
  cmp_item_row(): comparators(0), n(0) {}
  ~cmp_item_row();
  void store_value(Item *item);
  inline void alloc_comparators();
  int cmp(Item *arg);
  int compare(cmp_item *arg);
  cmp_item *make_same();
  void store_value_by_template(THD *thd, cmp_item *tmpl, Item *);
  friend void Item_func_in::fix_length_and_dec();
};


class in_row :public in_vector
{
  cmp_item_row tmp;
public:
  in_row(THD *thd, uint elements, Item *);
  ~in_row();
  void set(uint pos,Item *item);
  uchar *get_value(Item *item);
  friend void Item_func_in::fix_length_and_dec();
  Item_result result_type() { return ROW_RESULT; }
};

/* Functions used by where clause */
class Item_func_null_predicate :public Item_bool_func
{
protected:
  SEL_TREE *get_func_mm_tree(RANGE_OPT_PARAM *param,
                             Field *field, Item *value)
  {
    DBUG_ENTER("Item_func_null_predicate::get_func_mm_tree");
    DBUG_RETURN(get_mm_parts(param, field, functype(), value));
  }
  SEL_ARG *get_mm_leaf(RANGE_OPT_PARAM *param, Field *field,
                       KEY_PART *key_part,
                       Item_func::Functype type, Item *value);
public:
  Item_func_null_predicate(THD *thd, Item *a): Item_bool_func(thd, a) { }
  void add_key_fields(JOIN *join, KEY_FIELD **key_fields, uint *and_level,
                      table_map usable_tables, SARGABLE_PARAM **sargables);
  SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
  {
    DBUG_ENTER("Item_func_null_predicate::get_mm_tree");
    SEL_TREE *ftree= get_full_func_mm_tree_for_args(param, args[0], NULL);
    if (!ftree)
      ftree= Item_func::get_mm_tree(param, cond_ptr);
    DBUG_RETURN(ftree);
  }
  CHARSET_INFO *compare_collation() const
  { return args[0]->collation.collation; }
  void fix_length_and_dec() { decimals=0; max_length=1; maybe_null=0; }
  bool count_sargable_conds(uchar *arg);
};


class Item_func_isnull :public Item_func_null_predicate
{
public:
  Item_func_isnull(THD *thd, Item *a): Item_func_null_predicate(thd, a) {}
  longlong val_int();
  enum Functype functype() const { return ISNULL_FUNC; }
  void fix_length_and_dec()
  {
    Item_func_null_predicate::fix_length_and_dec();
    update_used_tables();
  }
  const char *func_name() const { return "isnull"; }
  /* Optimize case of not_null_column IS NULL */
  virtual void update_used_tables()
  {
    if (!args[0]->maybe_null)
    {
      used_tables_cache= 0;			/* is always false */
      const_item_cache= 1;
    }
    else
    {
      args[0]->update_used_tables();
      used_tables_cache= args[0]->used_tables();
      const_item_cache= args[0]->const_item();
    }
  }
  COND *remove_eq_conds(THD *thd, Item::cond_result *cond_value,
                        bool top_level);
  table_map not_null_tables() const { return 0; }
  Item *neg_transformer(THD *thd);
};

/* Functions used by HAVING for rewriting IN subquery */

class Item_in_subselect;

/* 
  This is like IS NOT NULL but it also remembers if it ever has
  encountered a NULL.
*/
class Item_is_not_null_test :public Item_func_isnull
{
  Item_in_subselect* owner;
public:
  Item_is_not_null_test(THD *thd, Item_in_subselect* ow, Item *a):
    Item_func_isnull(thd, a), owner(ow)
  {}
  enum Functype functype() const { return ISNOTNULLTEST_FUNC; }
  longlong val_int();
  const char *func_name() const { return "<is_not_null_test>"; }
  void update_used_tables();
  /*
    we add RAND_TABLE_BIT to prevent moving this item from HAVING to WHERE
  */
  table_map used_tables() const
    { return used_tables_cache | RAND_TABLE_BIT; }
  bool const_item() const { return FALSE; }
};


class Item_func_isnotnull :public Item_func_null_predicate
{
  bool abort_on_null;
public:
  Item_func_isnotnull(THD *thd, Item *a):
    Item_func_null_predicate(thd, a), abort_on_null(0)
  { }
  longlong val_int();
  enum Functype functype() const { return ISNOTNULL_FUNC; }
  const char *func_name() const { return "isnotnull"; }
  table_map not_null_tables() const
  { return abort_on_null ? not_null_tables_cache : 0; }
  Item *neg_transformer(THD *thd);
  virtual void print(String *str, enum_query_type query_type);
  void top_level_item() { abort_on_null=1; }
};


class Item_func_like :public Item_bool_func2
{
  // Turbo Boyer-Moore data
  bool        canDoTurboBM;	// pattern is '%abcd%' case
  const char* pattern;
  int         pattern_len;

  // TurboBM buffers, *this is owner
  int* bmGs; //   good suffix shift table, size is pattern_len + 1
  int* bmBc; // bad character shift table, size is alphabet_size

  void turboBM_compute_suffixes(int* suff);
  void turboBM_compute_good_suffix_shifts(int* suff);
  void turboBM_compute_bad_character_shifts();
  bool turboBM_matches(const char* text, int text_len) const;
  enum { alphabet_size = 256 };

  Item *escape_item;

  bool escape_used_in_parsing;
  bool use_sampling;

  DTCollation cmp_collation;
  String cmp_value1, cmp_value2;
  bool with_sargable_pattern() const;
protected:
  SEL_TREE *get_func_mm_tree(RANGE_OPT_PARAM *param,
                             Field *field, Item *value)
  {
    DBUG_ENTER("Item_func_like::get_func_mm_tree");
    DBUG_RETURN(get_mm_parts(param, field, LIKE_FUNC, value));
  }
  SEL_ARG *get_mm_leaf(RANGE_OPT_PARAM *param, Field *field,
                       KEY_PART *key_part,
                       Item_func::Functype type, Item *value);
public:
  int escape;

  Item_func_like(THD *thd, Item *a, Item *b, Item *escape_arg, bool escape_used):
    Item_bool_func2(thd, a, b), canDoTurboBM(FALSE), pattern(0), pattern_len(0),
    bmGs(0), bmBc(0), escape_item(escape_arg),
    escape_used_in_parsing(escape_used), use_sampling(0) {}
  longlong val_int();
  enum Functype functype() const { return LIKE_FUNC; }
  void print(String *str, enum_query_type query_type)
  {
    Item_func::print_op(str, query_type);
  }
  CHARSET_INFO *compare_collation() const
  { return cmp_collation.collation; }
  cond_result eq_cmp_result() const
  {
    /**
      We cannot always rewrite conditions as follows:
        from:  WHERE expr1=const AND expr1 LIKE expr2
        to:    WHERE expr1=const AND const LIKE expr2
      or
        from:  WHERE expr1=const AND expr2 LIKE expr1
        to:    WHERE expr1=const AND expr2 LIKE const

      because LIKE works differently comparing to the regular "=" operator:

      1. LIKE performs a stricter one-character-to-one-character comparison
         and does not recognize contractions and expansions.
         Replacing "expr1" to "const in LIKE would make the condition
         stricter in case of a complex collation.

      2. LIKE does not ignore trailing spaces and thus works differently
         from the "=" operator in case of "PAD SPACE" collations
         (which are the majority in MariaDB). So, for "PAD SPACE" collations:

         - expr1=const       - ignores trailing spaces
         - const LIKE expr2  - does not ignore trailing spaces
         - expr2 LIKE const  - does not ignore trailing spaces

      Allow only "binary" for now.
      It neither ignores trailing spaces nor has contractions/expansions.

      TODO:
      We could still replace "expr1" to "const" in "expr1 LIKE expr2"
      in case of a "PAD SPACE" collation, but only if "expr2" has '%'
      at the end.         
    */
    return compare_collation() == &my_charset_bin ? COND_TRUE : COND_OK;
  }
  void add_key_fields(JOIN *join, KEY_FIELD **key_fields, uint *and_level,
                      table_map usable_tables, SARGABLE_PARAM **sargables);
  SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr)
  {
    return with_sargable_pattern() ?
           Item_bool_func2::get_mm_tree(param, cond_ptr) :
           Item_func::get_mm_tree(param, cond_ptr);
  }
  Item* propagate_equal_fields(THD *thd, const Context &ctx, COND_EQUAL *cond)
  {
    /*
      LIKE differs from the regular comparison operator ('=') in the following:
      - LIKE never ignores trailing spaces (even for PAD SPACE collations)
        Propagation of equal fields with a PAD SPACE collation into LIKE
        is not safe.
        Example:
          WHERE a='a ' AND a LIKE 'a'     - returns true for 'a'
        cannot be rewritten to:
          WHERE a='a ' AND 'a ' LIKE 'a'  - returns false for 'a'
        Note, binary collations in MySQL/MariaDB, e.g. latin1_bin,
        still have the PAD SPACE attribute and ignore trailing spaces!
      - LIKE does not take into account contractions, expansions,
        and ignorable characters.
        Propagation of equal fields with contractions/expansions/ignorables
        is also not safe.

      It's safe to propagate my_charset_bin (BINARY/VARBINARY/BLOB) values,
      because they do not ignore trailing spaces and have one-to-one mapping
      between a string and its weights.
      The below condition should be true only for my_charset_bin
      (as of version 10.1.7).
    */
    uint flags= Item_func_like::compare_collation()->state;
    if ((flags & MY_CS_NOPAD) && !(flags & MY_CS_NON1TO1))
      Item_args::propagate_equal_fields(thd,
                                        Context(ANY_SUBST,
                                                STRING_RESULT,
                                                compare_collation()),
                                        cond);
    return this;
  }
  const char *func_name() const { return "like"; }
  bool fix_fields(THD *thd, Item **ref);
  void fix_length_and_dec()
  {
    max_length= 1;
    agg_arg_charsets_for_comparison(cmp_collation, args, 2);
  }
  void cleanup();

  bool find_selective_predicates_list_processor(uchar *arg);
};


class Regexp_processor_pcre
{
  pcre *m_pcre;
  bool m_conversion_is_needed;
  bool m_is_const;
  int m_library_flags;
  CHARSET_INFO *m_data_charset;
  CHARSET_INFO *m_library_charset;
  String m_prev_pattern;
  int m_pcre_exec_rc;
  int m_SubStrVec[30];
  uint m_subpatterns_needed;
  void pcre_exec_warn(int rc) const;
  int pcre_exec_with_warn(const pcre *code, const pcre_extra *extra,
                          const char *subject, int length, int startoffset,
                          int options, int *ovector, int ovecsize);
public:
  String *convert_if_needed(String *src, String *converter);
  String subject_converter;
  String pattern_converter;
  String replace_converter;
  Regexp_processor_pcre() :
    m_pcre(NULL), m_conversion_is_needed(true), m_is_const(0),
    m_library_flags(0),
    m_data_charset(&my_charset_utf8_general_ci),
    m_library_charset(&my_charset_utf8_general_ci),
    m_subpatterns_needed(0)
  {}
  int default_regex_flags();
  void init(CHARSET_INFO *data_charset, int extra_flags, uint nsubpatterns_arg)
  {
    m_library_flags= default_regex_flags() | extra_flags |
                    (data_charset != &my_charset_bin ?
                     (PCRE_UTF8 | PCRE_UCP) : 0) |
                    ((data_charset->state &
                     (MY_CS_BINSORT | MY_CS_CSSORT)) ? 0 : PCRE_CASELESS);

    // Convert text data to utf-8.
    m_library_charset= data_charset == &my_charset_bin ?
                       &my_charset_bin : &my_charset_utf8_general_ci;

    m_conversion_is_needed= (data_charset != &my_charset_bin) &&
                            !my_charset_same(data_charset, m_library_charset);
    m_subpatterns_needed= nsubpatterns_arg;
  }
  void fix_owner(Item_func *owner, Item *subject_arg, Item *pattern_arg);
  bool compile(String *pattern, bool send_error);
  bool compile(Item *item, bool send_error);
  bool recompile(Item *item)
  {
    return !m_is_const && compile(item, false);
  }
  bool exec(const char *str, int length, int offset);
  bool exec(String *str, int offset, uint n_result_offsets_to_convert);
  bool exec(Item *item, int offset, uint n_result_offsets_to_convert);
  bool match() const { return m_pcre_exec_rc < 0 ? 0 : 1; }
  int nsubpatterns() const { return m_pcre_exec_rc <= 0 ? 0 : m_pcre_exec_rc; }
  int subpattern_start(int n) const
  {
    return m_pcre_exec_rc <= 0 ? 0 : m_SubStrVec[n * 2];
  }
  int subpattern_end(int n) const
  {
    return m_pcre_exec_rc <= 0 ? 0 : m_SubStrVec[n * 2 + 1];
  }
  int subpattern_length(int n) const
  {
    return subpattern_end(n) - subpattern_start(n);
  }
  void cleanup()
  {
    if (m_pcre)
    {
      pcre_free(m_pcre);
      m_pcre= NULL;
    }
    m_prev_pattern.length(0);
  }
  bool is_compiled() const { return m_pcre != NULL; }
  bool is_const() const { return m_is_const; }
  void set_const(bool arg) { m_is_const= arg; }
  CHARSET_INFO * library_charset() const { return m_library_charset; }
};


class Item_func_regex :public Item_bool_func
{
  Regexp_processor_pcre re;
  DTCollation cmp_collation;
public:
  Item_func_regex(THD *thd, Item *a, Item *b): Item_bool_func(thd, a, b)
  {}
  void cleanup()
  {
    DBUG_ENTER("Item_func_regex::cleanup");
    Item_bool_func::cleanup();
    re.cleanup();
    DBUG_VOID_RETURN;
  }
  longlong val_int();
  void fix_length_and_dec();
  const char *func_name() const { return "regexp"; }

  virtual inline void print(String *str, enum_query_type query_type)
  {
    print_op(str, query_type);
  }

  CHARSET_INFO *compare_collation() const { return cmp_collation.collation; }
};


class Item_func_regexp_instr :public Item_int_func
{
  Regexp_processor_pcre re;
  DTCollation cmp_collation;
public:
  Item_func_regexp_instr(THD *thd, Item *a, Item *b): Item_int_func(thd, a, b)
  {}
  void cleanup()
  {
    DBUG_ENTER("Item_func_regexp_instr::cleanup");
    Item_int_func::cleanup();
    re.cleanup();
    DBUG_VOID_RETURN;
  }
  longlong val_int();
  void fix_length_and_dec();
  const char *func_name() const { return "regexp_instr"; }
};


typedef class Item COND;

class Item_cond :public Item_bool_func
{
protected:
  List<Item> list;
  bool abort_on_null;
  table_map and_tables_cache;

public:
  /* Item_cond() is only used to create top level items */
  Item_cond(THD *thd): Item_bool_func(thd), abort_on_null(1)
  { const_item_cache=0; }
  Item_cond(THD *thd, Item *i1, Item *i2);
  Item_cond(THD *thd, Item_cond *item);
  Item_cond(THD *thd, List<Item> &nlist):
    Item_bool_func(thd), list(nlist), abort_on_null(0) {}
  bool add(Item *item, MEM_ROOT *root)
  {
    DBUG_ASSERT(item);
    return list.push_back(item, root);
  }
  bool add_at_head(Item *item, MEM_ROOT *root)
  {
    DBUG_ASSERT(item);
    return list.push_front(item, root);
  }
  void add_at_head(List<Item> *nlist)
  {
    DBUG_ASSERT(nlist->elements);
    list.prepend(nlist);
  }
  void add_at_end(List<Item> *nlist)
  {
    DBUG_ASSERT(nlist->elements);
    list.append(nlist);
  }
  bool fix_fields(THD *, Item **ref);
  void fix_after_pullout(st_select_lex *new_parent, Item **ref);

  enum Type type() const { return COND_ITEM; }
  List<Item>* argument_list() { return &list; }
  table_map used_tables() const;
  void update_used_tables()
  {
    used_tables_and_const_cache_init();
    used_tables_and_const_cache_update_and_join(list);
  }
  COND *build_equal_items(THD *thd, COND_EQUAL *inherited,
                          bool link_item_fields,
                          COND_EQUAL **cond_equal_ref);
  COND *remove_eq_conds(THD *thd, Item::cond_result *cond_value,
                        bool top_level);
  void add_key_fields(JOIN *join, KEY_FIELD **key_fields,
                      uint *and_level, table_map usable_tables,
                      SARGABLE_PARAM **sargables);
  SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr);
  virtual void print(String *str, enum_query_type query_type);
  void split_sum_func(THD *thd, Item **ref_pointer_array, List<Item> &fields,
                      uint flags);
  friend int setup_conds(THD *thd, TABLE_LIST *tables, TABLE_LIST *leaves,
                         COND **conds);
  void top_level_item() { abort_on_null=1; }
  bool top_level() { return abort_on_null; }
  void copy_andor_arguments(THD *thd, Item_cond *item);
  bool walk(Item_processor processor, bool walk_subquery, uchar *arg);
  Item *transform(THD *thd, Item_transformer transformer, uchar *arg);
  void traverse_cond(Cond_traverser, void *arg, traverse_order order);
  void neg_arguments(THD *thd);
  enum_field_types field_type() const { return MYSQL_TYPE_LONGLONG; }
  Item* propagate_equal_fields(THD *, const Context &, COND_EQUAL *);
  Item *compile(THD *thd, Item_analyzer analyzer, uchar **arg_p,
                Item_transformer transformer, uchar *arg_t);
  bool eval_not_null_tables(uchar *opt_arg);
};

template <template<class> class LI, class T> class Item_equal_iterator;

/*
  The class Item_equal is used to represent conjunctions of equality
  predicates of the form field1 = field2, and field=const in where
  conditions and on expressions.

  All equality predicates of the form field1=field2 contained in a
  conjunction are substituted for a sequence of items of this class.
  An item of this class Item_equal(f1,f2,...fk) represents a
  multiple equality f1=f2=...=fk.

  If a conjunction contains predicates f1=f2 and f2=f3, a new item of
  this class is created Item_equal(f1,f2,f3) representing the multiple
  equality f1=f2=f3 that substitutes the above equality predicates in
  the conjunction.
  A conjunction of the predicates f2=f1 and f3=f1 and f3=f2 will be
  substituted for the item representing the same multiple equality
  f1=f2=f3.
  An item Item_equal(f1,f2) can appear instead of a conjunction of 
  f2=f1 and f1=f2, or instead of just the predicate f1=f2.

  An item of the class Item_equal inherits equalities from outer 
  conjunctive levels.

  Suppose we have a where condition of the following form:
  WHERE f1=f2 AND f3=f4 AND f3=f5 AND ... AND (...OR (f1=f3 AND ...)).
  In this case:
    f1=f2 will be substituted for Item_equal(f1,f2);
    f3=f4 and f3=f5  will be substituted for Item_equal(f3,f4,f5);
    f1=f3 will be substituted for Item_equal(f1,f2,f3,f4,f5);

  An object of the class Item_equal can contain an optional constant
  item c. Then it represents a multiple equality of the form 
  c=f1=...=fk.

  Objects of the class Item_equal are used for the following:

  1. An object Item_equal(t1.f1,...,tk.fk) allows us to consider any
  pair of tables ti and tj as joined by an equi-condition.
  Thus it provide us with additional access paths from table to table.

  2. An object Item_equal(t1.f1,...,tk.fk) is applied to deduce new
  SARGable predicates:
    f1=...=fk AND P(fi) => f1=...=fk AND P(fi) AND P(fj).
  It also can give us additional index scans and can allow us to
  improve selectivity estimates.

  3. An object Item_equal(t1.f1,...,tk.fk) is used to optimize the 
  selected execution plan for the query: if table ti is accessed 
  before the table tj then in any predicate P in the where condition
  the occurrence of tj.fj is substituted for ti.fi. This can allow
  an evaluation of the predicate at an earlier step.

  When feature 1 is supported they say that join transitive closure 
  is employed.
  When feature 2 is supported they say that search argument transitive
  closure is employed.
  Both features are usually supported by preprocessing original query and
  adding additional predicates.
  We do not just add predicates, we rather dynamically replace some
  predicates that can not be used to access tables in the investigated
  plan for those, obtained by substitution of some fields for equal fields,
  that can be used.     

  Prepared Statements/Stored Procedures note: instances of class
  Item_equal are created only at the time a PS/SP is executed and
  are deleted in the end of execution. All changes made to these
  objects need not be registered in the list of changes of the parse
  tree and do not harm PS/SP re-execution.

  Item equal objects are employed only at the optimize phase. Usually they are
  not supposed to be evaluated.  Yet in some cases we call the method val_int()
  for them. We have to take care of restricting the predicate such an
  object represents f1=f2= ...=fn to the projection of known fields fi1=...=fik.
*/

class Item_equal: public Item_bool_func
{
  /*
    The list of equal items. Currently the list can contain:
     - Item_fields items for references to table columns
     - Item_direct_view_ref items for references to view columns
     - one const item

    If the list contains a constant item this item is always first in the list.
    The list contains at least two elements.
    Currently all Item_fields/Item_direct_view_ref items in the list should
    refer to table columns with equavalent type definitions. In particular
    if these are string columns they should have the same charset/collation.

    Use objects of the companion class Item_equal_fields_iterator to iterate
    over all items from the list of the Item_field/Item_direct_view_ref classes.
  */ 
  List<Item> equal_items; 
  /* 
     TRUE <-> one of the items is a const item.
     Such item is always first in in the equal_items list
  */
  bool with_const;        
  /* 
    The field eval_item is used when this item is evaluated
    with the method val_int()
  */  
  cmp_item *eval_item;
  /*
    This initially is set to FALSE. It becomes TRUE when this item is evaluated
    as being always false. If the flag is TRUE the contents of the list 
    the equal_items should be ignored.
  */
  bool cond_false;
  /*
    This initially is set to FALSE. It becomes TRUE when this item is evaluated
    as being always true. If the flag is TRUE the contents of the list 
    the equal_items should be ignored.
  */
  bool cond_true;
  /*
    For Item_equal objects inside an OR clause: one of the fields that were
    used in the original equality.
  */
  Item_field *context_field;

  bool link_equal_fields;

  Item_result m_compare_type;
  CHARSET_INFO *m_compare_collation;
  String cmp_value1, cmp_value2;
public:

  COND_EQUAL *upper_levels;       /* multiple equalities of upper and levels */

  Item_equal(THD *thd, Item *f1, Item *f2, bool with_const_item);
  Item_equal(THD *thd, Item_equal *item_equal);
  /* Currently the const item is always the first in the list of equal items */
  inline Item* get_const() { return with_const ? equal_items.head() : NULL; }
  void add_const(THD *thd, Item *c);
  /** Add a non-constant item to the multiple equality */
  void add(Item *f, MEM_ROOT *root) { equal_items.push_back(f, root); }
  bool contains(Field *field);
  Item* get_first(struct st_join_table *context, Item *field);
  /** Get number of field items / references to field items in this object */   
  uint n_field_items() { return equal_items.elements - MY_TEST(with_const); }
  void merge(THD *thd, Item_equal *item);
  bool merge_with_check(THD *thd, Item_equal *equal_item, bool save_merged);
  void merge_into_list(THD *thd, List<Item_equal> *list, bool save_merged,
                      bool only_intersected);
  void update_const(THD *thd);
  enum Functype functype() const { return MULT_EQUAL_FUNC; }
  longlong val_int(); 
  const char *func_name() const { return "multiple equal"; }
  void sort(Item_field_cmpfunc compare, void *arg);
  void fix_length_and_dec();
  bool fix_fields(THD *thd, Item **ref);
  void update_used_tables();
  COND *build_equal_items(THD *thd, COND_EQUAL *inherited,
                          bool link_item_fields,
                          COND_EQUAL **cond_equal_ref);
  void add_key_fields(JOIN *join, KEY_FIELD **key_fields,
                      uint *and_level, table_map usable_tables,
                      SARGABLE_PARAM **sargables);
  SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr);
  bool walk(Item_processor processor, bool walk_subquery, uchar *arg);
  Item *transform(THD *thd, Item_transformer transformer, uchar *arg);
  virtual void print(String *str, enum_query_type query_type);
  Item_result compare_type() const { return m_compare_type; }
  CHARSET_INFO *compare_collation() const { return m_compare_collation; }

  void set_context_field(Item_field *ctx_field) { context_field= ctx_field; }
  void set_link_equal_fields(bool flag) { link_equal_fields= flag; }
  friend class Item_equal_fields_iterator;
  bool count_sargable_conds(uchar *arg);
  friend class Item_equal_iterator<List_iterator_fast,Item>;
  friend class Item_equal_iterator<List_iterator,Item>;
  friend Item *eliminate_item_equal(THD *thd, COND *cond,
                                    COND_EQUAL *upper_levels,
                                    Item_equal *item_equal);
  friend bool setup_sj_materialization_part1(struct st_join_table *tab);
  friend bool setup_sj_materialization_part2(struct st_join_table *tab);
}; 

class COND_EQUAL: public Sql_alloc
{
public:
  uint max_members;               /* max number of members the current level
                                     list and all lower level lists */ 
  COND_EQUAL *upper_levels;       /* multiple equalities of upper and levels */
  List<Item_equal> current_level; /* list of multiple equalities of 
                                     the current and level           */
  COND_EQUAL()
  { 
    upper_levels= 0;
  }
  COND_EQUAL(Item_equal *item, MEM_ROOT *mem_root)
   :upper_levels(0)
  {
    current_level.push_back(item, mem_root);
  }
  void copy(COND_EQUAL &cond_equal)
  {
    max_members= cond_equal.max_members;
    upper_levels= cond_equal.upper_levels;
    if (cond_equal.current_level.is_empty())
      current_level.empty();
    else
      current_level= cond_equal.current_level;
  }
};


/* 
  The template Item_equal_iterator is used to define classes
  Item_equal_fields_iterator and Item_equal_fields_iterator_slow.
  These are helper classes for the class Item equal
  Both classes are used to iterate over references to table/view columns
  from the list of equal items that included in an Item_equal object. 
  The second class supports the operation of removal of the current member
  from the list when performing an iteration.
*/ 

template <template<class> class LI, typename T> class Item_equal_iterator
  : public LI<T>
{
protected:
  Item_equal *item_equal;
  Item *curr_item;
public:
  Item_equal_iterator<LI,T>(Item_equal &item_eq) 
    :LI<T> (item_eq.equal_items)
  {
    curr_item= NULL;
    item_equal= &item_eq;
    if (item_eq.with_const)
    {
      LI<T> *list_it= this;
      curr_item=  (*list_it)++;
    }
  }
  Item* operator++(int)
  { 
    LI<T> *list_it= this;
    curr_item= (*list_it)++;
    return curr_item;
  }
  void rewind(void) 
  { 
    LI<T> *list_it= this;
    list_it->rewind();
    if (item_equal->with_const)
      curr_item= (*list_it)++;
  }  
  Field *get_curr_field()
  {
    Item_field *item= (Item_field *) (curr_item->real_item());
     return item->field;
  }  
};

typedef  Item_equal_iterator<List_iterator_fast,Item >  Item_equal_iterator_fast;

class Item_equal_fields_iterator
  :public Item_equal_iterator_fast
{
public:
  Item_equal_fields_iterator(Item_equal &item_eq) 
    :Item_equal_iterator_fast(item_eq)
  { }
  Item ** ref()
  {
    return List_iterator_fast<Item>::ref();
  }
};

typedef Item_equal_iterator<List_iterator,Item > Item_equal_iterator_iterator_slow;

class Item_equal_fields_iterator_slow
  :public Item_equal_iterator_iterator_slow
{
public:
  Item_equal_fields_iterator_slow(Item_equal &item_eq) 
    :Item_equal_iterator_iterator_slow(item_eq)
  { }
  void remove()
  {
    List_iterator<Item>::remove();
  }
};


class Item_cond_and :public Item_cond
{
public:
  COND_EQUAL m_cond_equal;  /* contains list of Item_equal objects for 
                               the current and level and reference
                               to multiple equalities of upper and levels */  
  Item_cond_and(THD *thd): Item_cond(thd) {}
  Item_cond_and(THD *thd, Item *i1,Item *i2): Item_cond(thd, i1, i2) {}
  Item_cond_and(THD *thd, Item_cond_and *item): Item_cond(thd, item) {}
  Item_cond_and(THD *thd, List<Item> &list_arg): Item_cond(thd, list_arg) {}
  enum Functype functype() const { return COND_AND_FUNC; }
  longlong val_int();
  const char *func_name() const { return "and"; }
  table_map not_null_tables() const
  { return abort_on_null ? not_null_tables_cache: and_tables_cache; }
  Item *copy_andor_structure(THD *thd);
  Item *neg_transformer(THD *thd);
  void mark_as_condition_AND_part(TABLE_LIST *embedding);
  virtual uint exists2in_reserved_items() { return list.elements; };
  bool walk_top_and(Item_processor processor, uchar *arg);
  COND *build_equal_items(THD *thd, COND_EQUAL *inherited,
                          bool link_item_fields,
                          COND_EQUAL **cond_equal_ref);
  void add_key_fields(JOIN *join, KEY_FIELD **key_fields, uint *and_level,
                      table_map usable_tables, SARGABLE_PARAM **sargables);
  SEL_TREE *get_mm_tree(RANGE_OPT_PARAM *param, Item **cond_ptr);
};

inline bool is_cond_and(Item *item)
{
  if (item->type() != Item::COND_ITEM)
    return FALSE;

  Item_cond *cond_item= (Item_cond*) item;
  return (cond_item->functype() == Item_func::COND_AND_FUNC);
}

class Item_cond_or :public Item_cond
{
public:
  Item_cond_or(THD *thd): Item_cond(thd) {}
  Item_cond_or(THD *thd, Item *i1,Item *i2): Item_cond(thd, i1, i2) {}
  Item_cond_or(THD *thd, Item_cond_or *item): Item_cond(thd, item) {}
  Item_cond_or(THD *thd, List<Item> &list_arg): Item_cond(thd, list_arg) {}
  enum Functype functype() const { return COND_OR_FUNC; }
  longlong val_int();
  const char *func_name() const { return "or"; }
  table_map not_null_tables() const { return and_tables_cache; }
  Item *copy_andor_structure(THD *thd);
  Item *neg_transformer(THD *thd);
};

class Item_func_dyncol_check :public Item_bool_func
{
public:
  Item_func_dyncol_check(THD *thd, Item *str): Item_bool_func(thd, str) {}
  longlong val_int();
  const char *func_name() const { return "column_check"; }
};

class Item_func_dyncol_exists :public Item_bool_func
{
public:
  Item_func_dyncol_exists(THD *thd, Item *str, Item *num):
    Item_bool_func(thd, str, num) {}
  longlong val_int();
  const char *func_name() const { return "column_exists"; }
};

inline bool is_cond_or(Item *item)
{
  if (item->type() != Item::COND_ITEM)
    return FALSE;

  Item_cond *cond_item= (Item_cond*) item;
  return (cond_item->functype() == Item_func::COND_OR_FUNC);
}

Item *and_expressions(Item *a, Item *b, Item **org_item);

longlong get_datetime_value(THD *thd, Item ***item_arg, Item **cache_arg,
                            enum_field_types f_type, bool *is_null);


class Comp_creator
{
public:
  Comp_creator() {}                           /* Remove gcc warning */
  virtual ~Comp_creator() {}                  /* Remove gcc warning */
  /**
    Create operation with given arguments.
  */
  virtual Item_bool_rowready_func2* create(THD *thd, Item *a, Item *b)
                                           const = 0;
  /**
    Create operation with given arguments in swap order.
  */
  virtual Item_bool_rowready_func2* create_swap(THD *thd, Item *a, Item *b)
                                                const = 0;
  virtual const char* symbol(bool invert) const = 0;
  virtual bool eqne_op() const = 0;
  virtual bool l_op() const = 0;
};

class Eq_creator :public Comp_creator
{
public:
  Eq_creator() {}                             /* Remove gcc warning */
  virtual ~Eq_creator() {}                    /* Remove gcc warning */
  Item_bool_rowready_func2* create(THD *thd, Item *a, Item *b) const;
  Item_bool_rowready_func2* create_swap(THD *thd, Item *a, Item *b) const;
  const char* symbol(bool invert) const { return invert? "<>" : "="; }
  bool eqne_op() const { return 1; }
  bool l_op() const { return 0; }
};

class Ne_creator :public Comp_creator
{
public:
  Ne_creator() {}                             /* Remove gcc warning */
  virtual ~Ne_creator() {}                    /* Remove gcc warning */
  Item_bool_rowready_func2* create(THD *thd, Item *a, Item *b) const;
  Item_bool_rowready_func2* create_swap(THD *thd, Item *a, Item *b) const;
  const char* symbol(bool invert) const { return invert? "=" : "<>"; }
  bool eqne_op() const { return 1; }
  bool l_op() const { return 0; }
};

class Gt_creator :public Comp_creator
{
public:
  Gt_creator() {}                             /* Remove gcc warning */
  virtual ~Gt_creator() {}                    /* Remove gcc warning */
  Item_bool_rowready_func2* create(THD *thd, Item *a, Item *b) const;
  Item_bool_rowready_func2* create_swap(THD *thd, Item *a, Item *b) const;
  const char* symbol(bool invert) const { return invert? "<=" : ">"; }
  bool eqne_op() const { return 0; }
  bool l_op() const { return 0; }
};

class Lt_creator :public Comp_creator
{
public:
  Lt_creator() {}                             /* Remove gcc warning */
  virtual ~Lt_creator() {}                    /* Remove gcc warning */
  Item_bool_rowready_func2* create(THD *thd, Item *a, Item *b) const;
  Item_bool_rowready_func2* create_swap(THD *thd, Item *a, Item *b) const;
  const char* symbol(bool invert) const { return invert? ">=" : "<"; }
  bool eqne_op() const { return 0; }
  bool l_op() const { return 1; }
};

class Ge_creator :public Comp_creator
{
public:
  Ge_creator() {}                             /* Remove gcc warning */
  virtual ~Ge_creator() {}                    /* Remove gcc warning */
  Item_bool_rowready_func2* create(THD *thd, Item *a, Item *b) const;
  Item_bool_rowready_func2* create_swap(THD *thd, Item *a, Item *b) const;
  const char* symbol(bool invert) const { return invert? "<" : ">="; }
  bool eqne_op() const { return 0; }
  bool l_op() const { return 0; }
};

class Le_creator :public Comp_creator
{
public:
  Le_creator() {}                             /* Remove gcc warning */
  virtual ~Le_creator() {}                    /* Remove gcc warning */
  Item_bool_rowready_func2* create(THD *thd, Item *a, Item *b) const;
  Item_bool_rowready_func2* create_swap(THD *thd, Item *a, Item *b) const;
  const char* symbol(bool invert) const { return invert? ">" : "<="; }
  bool eqne_op() const { return 0; }
  bool l_op() const { return 1; }
};

/*
  These need definitions from this file but the variables are defined
  in mysqld.h. The variables really belong in this component, but for
  the time being we leave them in mysqld.cc to avoid merge problems.
*/
extern Eq_creator eq_creator;
extern Ne_creator ne_creator;
extern Gt_creator gt_creator;
extern Lt_creator lt_creator;
extern Ge_creator ge_creator;
extern Le_creator le_creator;

#endif /* ITEM_CMPFUNC_INCLUDED */