Add example for writing an SQL analysis pass #10871

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1. alamb

   added

   enhancementNew feature or requestNew feature or request

   on Jun 11, 2024
2. LorrensP-2158466 commented on Jun 11, 2024

   

   LorrensP-2158466

   on Jun 11, 2024

   Contributor

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   I like the Join count analysis, I had to do this in my project (mentioned in #10808) in a really hacky way. We can have 2 sorts of counts:

   1. Count every individual join
   2. Count all groups of joins (subsequent joins that are related) with their respective count(this would have been useful for me)

   I do have a question.
   How can we show these results? Because Analyzer rules only return transformed LogicalPlans, or do I understand something in a wrong way?
3. alamb commented on Jun 15, 2024

   

   alamb

   on Jun 15, 2024

   ContributorAuthor

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   Thank you @LorrensP-2158466 -- sorry for the delay . I have been traveling

   I do have a question.
   How can we show these results? Because Analyzer rules only return transformed LogicalPlans, or do I understand something in a wrong way?

   I think in an example, we can use println! which is what we do in other examples:

   datafusion/datafusion-examples/examples/rewrite_expr.rs

   Lines 45 to 48 in 3773fb7

   	println!(
   	"Unoptimized Logical Plan:\n\n{}\n",
   	logical_plan.display_indent()
   	);

   Normally the idea is to give a well documented example that shows the basic pattern that people can start with

   For this one, maybe you could show how to use TreeNode::apply to walk the tree. Something like (totally untested)

   let mut join_count = 0;
   plan.apply(|child| {
     if matches!(child, LogicalPlan::Join(_)) {
       join_count += 1;
     }
   });
   
   println!("Found {join_count} joins in the plan");
4. LorrensP-2158466 commented on Jun 15, 2024

   

   LorrensP-2158466

   on Jun 15, 2024

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   Thanks for the reply!

   That's exactly what I have made, I'll open up a PR later today or tomorrow.
5. alamb

   closed this as completedin #10938on Jun 18, 2024