Jefffrey commented on code in PR #5820:
URL: https://github.com/apache/arrow-datafusion/pull/5820#discussion_r1155097167
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datafusion/optimizer/src/type_coercion.rs:
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@@ -330,8 +330,35 @@ impl TreeNodeRewriter for TypeCoercionRewriter {
}
}
Expr::Case(case) => {
- // all the result of then and else should be convert to a
common data type,
- // if they can be coercible to a common data type, return
error.
+ // Given expressions like:
+ //
+ // CASE a1
+ // WHEN a2 THEN b1
+ // WHEN a3 THEN b2
+ // ELSE b3
+ // END
+ //
+ // or:
+ //
+ // CASE
+ // WHEN x1 THEN b1
+ // WHEN x2 THEN b2
+ // ELSE b3
+ // END
+ //
+ // Then all aN (a1, a2, a3) must be converted to a common data
type in the first example
+ // (case-when expression coercion)
+ //
+ // And all bN (b1, b2, b3) must be converted to a common data
type in both examples
+ // (then-else expression coercion)
+ //
+ // If either fail to find a common data type, will return error
+
+ // prepare types
+ let case_type = match &case.expr {
+ None => Ok(None),
+ Some(expr) => expr.get_type(&self.schema).map(Some),
+ }?;
Review Comment:
Thanks that does look cleaner, will apply it
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