[GitHub] spark pull request #17330: [SPARK-19993][SQL][WIP] Caching logical plans con...

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

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

    https://github.com/apache/spark/pull/17330#discussion_r106758290
  
    --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/subquery.scala ---
    @@ -61,6 +63,36 @@ abstract class SubqueryExpression(
       }
     }
     
    +/**
    + * This expression is used to represent any form of subquery expression namely
    + * ListQuery, Exists and ScalarSubquery. This is only used to make sure the
    + * expression equality works properly when LogicalPlan.sameResult is called
    + * on plans containing SubqueryExpression(s). This is only a transient expression
    + * that only lives in the scope of sameResult function call. In other words, analyzer,
    + * optimizer or planner never sees this expression type during transformation of
    + * plans.
    + */
    +case class CanonicalizedSubqueryExpr(expr: SubqueryExpression)
    +  extends LeafExpression with Unevaluable {
    +  override def dataType: DataType = expr.dataType
    +  override def nullable: Boolean = expr.nullable
    +  override def toString: String = s"CanonicalizedSubqueryExpr(${expr.toString})"
    +
    +  // Hashcode is generated conservatively for now i.e it does not include the
    +  // sub query plan. Doing so causes issue when we canonicalize expressions to
    +  // re-order them based on hashcode.
    +  // TODO : improve the hashcode generation by considering the plan info.
    +  override def hashCode(): Int = {
    +    val state = Seq(children, this.getClass.getName)
    +    state.map(Objects.hashCode).foldLeft(0)((a, b) => 31 * a + b)
    --- End diff --
    
    can we write this imperatively


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