gabotechs commented on code in PR #24670:
URL: https://github.com/apache/datafusion/pull/24670#discussion_r3853980928
##########
datafusion/physical-plan/src/projection.rs:
##########
@@ -1030,7 +1030,8 @@ pub fn remove_unnecessary_projections(
}
/// Compare the inputs and outputs of the projection. All expressions must be
-/// columns without alias, and projection does not change the order of fields.
+/// columns without alias, the projection must not change the order of fields,
+/// and its output schema must match its input schema, including metadata.
Review Comment:
🤔 Why can't it change the order of fields? As long as the name is the same
one, that's what matters AFAIK.
##########
datafusion/physical-plan/src/projection.rs:
##########
@@ -1041,6 +1042,7 @@ fn is_projection_removable(projection: &ProjectionExec)
-> bool {
};
col.name() == proj_expr.alias && col.index() == idx
}) && exprs.len() == projection.input().schema().fields().len()
+ && projection.schema() == projection.input().schema()
Review Comment:
This might be putting more restrictions than just metadata equality. It
might be fine, but if we want to play it safe it could be better to just do `&&
projection.schema().metadata() == projection.input().schema().metadata()`
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