Aggregate plan schema build error if aggr exprs contain cast and column

Describe the bug

Execute below sqls in datafusion-cli

create table t (a int);
select max(a) as a1, max(cast(a, bigint)) as a2 from t;

will get error: Schema error: Schema contains duplicate unqualified field name "max(t.a)". I tried in postgres and it won't fail.

I've found root cause. it's due to aggregate plan output schema building.

datafusion/datafusion/expr/src/logical_plan/plan.rs

Lines 3492 to 3497 in 5258352

    
           qualified_fields.extend(exprlist_to_fields(aggr_expr.as_slice(), &input)?); 
        
           let schema = DFSchema::new_with_metadata( 
        
               qualified_fields, 
        
               input.schema().metadata().clone(), 
        
           )?;

It will call SchemaDisplay code.

datafusion/datafusion/expr/src/expr.rs

Lines 2799 to 2802 in 5258352

    
           // Cast expr is not shown to be consistent with Postgres and Spark <https://github.com/apache/datafusion/pull/3222> 
        
           Expr::Cast(Cast { expr, .. }) | Expr::TryCast(TryCast { expr, .. }) => { 
        
               write!(f, "{}", SchemaDisplay(expr)) 
        
           }

The schema name of cast expr is same with column expr.
But the comment says Cast expr is not shown to be consistent with Postgres and Spark. So I don't know what is the right fix.

To Reproduce

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Expected behavior

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Additional context

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Seems similar to #3353

I looked into #3353 a bit before, haven't gotten around to typing up my investigation/thoughts yet (hopefully soon)

Seems similar to #3353

I looked into #3353 a bit before, haven't gotten around to typing up my investigation/thoughts yet (hopefully soon)

Put my notes here: #3353 (comment)

However looking at it from the cast expr name would be valid too, since if we remove the aliases from the query, I think we'd still run into this problem.

Thanks for looking into it. As this issue is duplicate, feel free to close.

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Aggregate plan schema build error if aggr exprs contain cast and column #18975

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	qualified_fields.extend(exprlist_to_fields(aggr_expr.as_slice(), &input)?);

	let schema = DFSchema::new_with_metadata(
	qualified_fields,
	input.schema().metadata().clone(),
	)?;

	// Cast expr is not shown to be consistent with Postgres and Spark <https://github.com/apache/datafusion/pull/3222>
	Expr::Cast(Cast { expr, .. }) \| Expr::TryCast(TryCast { expr, .. }) => {
	write!(f, "{}", SchemaDisplay(expr))
	}

Aggregate plan schema build error if aggr exprs contain cast and column #18975

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Jefffrey commented on Nov 28, 2025

Jefffrey commented on Dec 2, 2025

lewiszlw commented on Dec 3, 2025

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