Github user gatorsmile commented on a diff in the pull request: https://github.com/apache/spark/pull/19977#discussion_r157899407 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/TypeCoercion.scala --- @@ -564,6 +565,16 @@ object TypeCoercion { NaNvl(Cast(l, DoubleType), r) case NaNvl(l, r) if r.dataType == NullType => NaNvl(l, Cast(r, l.dataType)) } + // This group needs to be transformed in a post order + .transformExpressionsUp { + // When all inputs in [[Concat]] are binary, coerces an output type to binary + case c @ Concat(children, _) --- End diff -- Create a new `TypeCoercion ` rule for it?
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