comphead commented on code in PR #12142:
URL: https://github.com/apache/datafusion/pull/12142#discussion_r1730134229
##########
datafusion/expr/src/logical_plan/builder.rs:
##########
@@ -1331,7 +1331,17 @@ pub fn validate_unique_names<'a>(
})
}
-/// Union two logical plans.
+/// Union two [`LogicalPlan`]s.
+///
+/// Constructs the UNION plan, but does not perform type-coercion. Therefore
the
+/// subtree expressions will not be properly typed until the optimizer pass.
+///
+/// If a properly typed UNION plan is needed, refer to
[`TypeCoercionRewriter::coerce_union`]
+/// or alternatively, merge the union input schema using
[`coerce_union_schema`] and
+/// apply the expression rewrite with [`coerce_plan_expr_for_schema`].
+///
+/// [`TypeCoercionRewriter::coerce_union`]:
https://docs.rs/datafusion-optimizer/latest/datafusion_optimizer/analyzer/type_coercion/struct.TypeCoercionRewriter.html#method.coerce_union
Review Comment:
👍
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