[GitHub] spark pull request: [SPARK-12841][SQL] fix cast in filter

[yhuai <gi...@git.apache.org>]

Github user yhuai commented on a diff in the pull request:

    https://github.com/apache/spark/pull/10781#discussion_r49949314
  
    --- Diff: sql/core/src/main/scala/org/apache/spark/sql/Column.scala ---
    @@ -133,6 +133,15 @@ class Column(protected[sql] val expr: Expression) extends Logging {
     
         case func: UnresolvedFunction => UnresolvedAlias(func, Some(func.prettyString))
     
    +    // If we have a top level Cast, there is a chance to give it a better alias, if there is a
    +    // NamedExpression under this Cast.
    +    case c: Cast => c.transformUp {
    +      case Cast(ne: NamedExpression, to) => UnresolvedAlias(Cast(ne, to))
    +    } match {
    +      case ne: NamedExpression => ne
    +      case other => Alias(expr, expr.prettyString)()
    +    }
    --- End diff --
    
    We use `transformUp` at here to make this logic equivalent with the original logic that we have in the `cast`, right (since we want to fix it in 1.6)? (in future, will it be possible to just use `cast Cast(ne: NamedExpression, to) => UnresolvedAlias(Cast(ne, to))`?)


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