yashaggarwal85d commented on code in PR #26558:
URL: https://github.com/apache/datafusion/pull/26558#discussion_r4399677703
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datafusion/optimizer/src/analyzer/type_coercion.rs:
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@@ -311,6 +311,65 @@ impl<'a> TypeCoercionRewriter<'a> {
self
}
+ /// Coerce a subquery whose outer plan has been coerced into `self.schema`.
+ ///
+ /// The subquery was coerced before its outer plan, against the types its
+ /// outer reference columns had when the plan was built. Coercing the outer
+ /// plan can change those types, for example for a `CASE` with `INT` and
+ /// `BIGINT` branches or a `UNION` of `INT` and `BIGINT` columns. In that
+ /// case the outer references take the new types and the subquery is
+ /// coerced again, so that its comparisons with them are coerced too.
+ fn coerce_subquery(&self, subquery: Subquery) -> Result<Subquery> {
Review Comment:
Agreed. The plan walk no longer goes into subqueries on its own. The
rewriter coerces a subquery when it reaches it, with the outer node's schema,
so every node gets coerced once (before, the subquery root was coerced twice)
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