fix: Ensure column names do not change with expand_views_at_output (#19019)

## Which issue does this PR close?

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- Closes #18818.

## Rationale for this change

<!--
Why are you proposing this change? If this is already explained clearly
in the issue then this section is not needed.
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your changes and offer better suggestions for fixes.
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Making the schema consistent whether having
`datafusion.optimizer.expand_views_at_output` on or off:

```sql
> create table t(a int, b varchar);

> set datafusion.optimizer.expand_views_at_output = true;

-- before
> select * from t;
+---+-----+
| a | t.b |
+---+-----+
+---+-----+

-- now
> select * from t;
+---+---+
| a | b |
+---+---+
+---+---+

```

## What changes are included in this PR?

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There is no need to duplicate the description in the issue here but it
is sometimes worth providing a summary of the individual changes in this
PR.
-->

- Added an alias when converting expressions.
- Added sqllogictests.

## Are these changes tested?

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1. Prevent the code from being accidentally broken by subsequent changes
2. Serve as another way to document the expected behavior of the code

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Yes.

## Are there any user-facing changes?

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updated before approving the PR.
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The column names when enabling
`datafusion.optimizer.expand_views_at_output` are now the same when
having it disabled.

<!--
If there are any breaking changes to public APIs, please add the `api
change` label.
-->

---------

Co-authored-by: Andrew Lamb <[email protected]>

Author: nuno-faria

datafusion/expr/src/expr_rewriter/mod.rs

@@ -260,7 +260,11 @@ fn coerce_exprs_for_schema(
                     }
                     #[expect(deprecated)]
                     Expr::Wildcard { .. } => Ok(expr),
-                    _ => expr.cast_to(new_type, src_schema),
+                    _ => {
+                        // maintain the original name when casting
+                        let name = dst_schema.field(idx).name();
+                        Ok(expr.cast_to(new_type, src_schema)?.alias(name))
+                    }
                 }
             } else {
                 Ok(expr)

datafusion/optimizer/src/analyzer/type_coercion.rs

@@ -1305,7 +1305,7 @@ mod test {
             true,
             plan.clone(),
             @r"
-        Projection: CAST(a AS LargeUtf8)
+        Projection: CAST(a AS LargeUtf8) AS a
           EmptyRelation: rows=0
         "
         )?;
@@ -1341,7 +1341,7 @@ mod test {
             true,
             plan.clone(),
             @r"
-        Projection: CAST(a AS LargeUtf8)
+        Projection: CAST(a AS LargeUtf8) AS a
           EmptyRelation: rows=0
         "
         )?;
@@ -1371,7 +1371,7 @@ mod test {
             true,
             sort_plan.clone(),
             @r"
-        Projection: CAST(a AS LargeUtf8)
+        Projection: CAST(a AS LargeUtf8) AS a
           Sort: a ASC NULLS FIRST
             Projection: a
               EmptyRelation: rows=0
@@ -1400,7 +1400,7 @@ mod test {
             true,
             plan.clone(),
             @r"
-        Projection: CAST(a AS LargeUtf8)
+        Projection: CAST(a AS LargeUtf8) AS a
           Sort: a ASC NULLS FIRST
             Projection: a
               EmptyRelation: rows=0
@@ -1436,7 +1436,7 @@ mod test {
             true,
             plan.clone(),
             @r"
-        Projection: CAST(a AS LargeBinary)
+        Projection: CAST(a AS LargeBinary) AS a
           EmptyRelation: rows=0
         "
         )?;
@@ -1493,7 +1493,7 @@ mod test {
             true,
             sort_plan.clone(),
             @r"
-        Projection: CAST(a AS LargeBinary)
+        Projection: CAST(a AS LargeBinary) AS a
           Sort: a ASC NULLS FIRST
             Projection: a
               EmptyRelation: rows=0
@@ -1524,7 +1524,7 @@ mod test {
             true,
             plan.clone(),
             @r"
-        Projection: CAST(a AS LargeBinary)
+        Projection: CAST(a AS LargeBinary) AS a
           Sort: a ASC NULLS FIRST
             Projection: a
               EmptyRelation: rows=0

datafusion/optimizer/tests/optimizer_integration.rs

@@ -538,14 +538,15 @@ fn recursive_cte_projection_pushdown() -> Result<()> {
     // columns from the base table and recursive table, eliminating unused columns
     assert_snapshot!(
         format!("{plan}"),
-        @r#"SubqueryAlias: nodes
-  RecursiveQuery: is_distinct=false
-    Projection: test.col_int32 AS id
-      TableScan: test projection=[col_int32]
-    Projection: CAST(CAST(nodes.id AS Int64) + Int64(1) AS Int32)
-      Filter: nodes.id < Int32(3)
-        TableScan: nodes projection=[id]
-"#
+        @r"
+    SubqueryAlias: nodes
+      RecursiveQuery: is_distinct=false
+        Projection: test.col_int32 AS id
+          TableScan: test projection=[col_int32]
+        Projection: CAST(CAST(nodes.id AS Int64) + Int64(1) AS Int32) AS id
+          Filter: nodes.id < Int32(3)
+            TableScan: nodes projection=[id]
+    "
     );
     Ok(())
 }
@@ -561,14 +562,16 @@ fn recursive_cte_with_aliased_self_reference() -> Result<()> {
 
     assert_snapshot!(
         format!("{plan}"),
-        @r#"SubqueryAlias: nodes
-  RecursiveQuery: is_distinct=false
-    Projection: test.col_int32 AS id
-      TableScan: test projection=[col_int32]
-    Projection: CAST(CAST(child.id AS Int64) + Int64(1) AS Int32)
-      SubqueryAlias: child
-        Filter: nodes.id < Int32(3)
-          TableScan: nodes projection=[id]"#,
+        @r"
+    SubqueryAlias: nodes
+      RecursiveQuery: is_distinct=false
+        Projection: test.col_int32 AS id
+          TableScan: test projection=[col_int32]
+        Projection: CAST(CAST(child.id AS Int64) + Int64(1) AS Int32) AS id
+          SubqueryAlias: child
+            Filter: nodes.id < Int32(3)
+              TableScan: nodes projection=[id]
+    ",
     );
     Ok(())
 }
@@ -620,15 +623,16 @@ fn recursive_cte_projection_pushdown_baseline() -> Result<()> {
     // and only the needed column is selected from the recursive table
     assert_snapshot!(
         format!("{plan}"),
-        @r#"SubqueryAlias: countdown
-  RecursiveQuery: is_distinct=false
-    Projection: test.col_int32 AS n
-      Filter: test.col_int32 = Int32(5)
-        TableScan: test projection=[col_int32]
-    Projection: CAST(CAST(countdown.n AS Int64) - Int64(1) AS Int32)
-      Filter: countdown.n > Int32(1)
-        TableScan: countdown projection=[n]
-"#
+        @r"
+    SubqueryAlias: countdown
+      RecursiveQuery: is_distinct=false
+        Projection: test.col_int32 AS n
+          Filter: test.col_int32 = Int32(5)
+            TableScan: test projection=[col_int32]
+        Projection: CAST(CAST(countdown.n AS Int64) - Int64(1) AS Int32) AS n
+          Filter: countdown.n > Int32(1)
+            TableScan: countdown projection=[n]
+    "
     );
     Ok(())
 }

datafusion/sqllogictest/test_files/cast.slt

@@ -89,3 +89,39 @@ select * from t0 where v0<1e100;
 
 statement ok
 drop table t0;
+
+
+# ensure that automatically casting with "datafusion.optimizer.expand_views_at_output" does not
+# change the column name
+
+statement ok
+create table t(a int, b varchar);
+
+statement ok
+set datafusion.optimizer.expand_views_at_output = true;
+
+query TT
+explain select * from t;
+----
+logical_plan
+01)Projection: t.a, CAST(t.b AS LargeUtf8) AS b
+02)--TableScan: t projection=[a, b]
+physical_plan
+01)ProjectionExec: expr=[a@0 as a, CAST(b@1 AS LargeUtf8) as b]
+02)--DataSourceExec: partitions=1, partition_sizes=[0]
+
+query TT
+explain select b from t;
+----
+logical_plan
+01)Projection: CAST(t.b AS LargeUtf8) AS b
+02)--TableScan: t projection=[b]
+physical_plan
+01)ProjectionExec: expr=[CAST(b@0 AS LargeUtf8) as b]
+02)--DataSourceExec: partitions=1, partition_sizes=[0]
+
+statement ok
+set datafusion.optimizer.expand_views_at_output = false;
+
+statement ok
+drop table t;