Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/8066#discussion_r46452998
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala
---
@@ -919,3 +920,63 @@ object RemoveLiteralFromGroupExpressions extends
Rule[LogicalPlan] {
a.copy(groupingExpressions = newGrouping)
}
}
+
+/**
+ * Remove the unnecessary evaluation from SortOrder, if they are already
in child's output.
+ *
+ * As an example, "select a + 1, b from t order by a + 1" will be analyzed
into:
+ * {{{
+ * Project(reference#2, b#0,
+ * Sort('a#1 + 1,
+ * Project(('a + 1).as("_c0")#2, b#0, a#1),
+ * Relation)
+ * }}}
+ * Then this rule can optimize it into:
+ * {{{
+ * Project(reference#2, b#0,
+ * Sort(reference#2,
+ * Project(('a + 1).as("_c0")#2, b#0, a#1),
+ * Relation)
+ * }}}
+ * Finally other optimize rules(column pruning, project collapse) can turn
it into:
+ * {{{
+ * Sort(reference#2,
+ * Project(('a + 1).as("_c0")#2, b#0),
+ * Relation)
+ * }}}
+ */
+object RemoveUnnecessarySortOrderEvaluation extends Rule[LogicalPlan] {
+
+ private def optimizeSortOrders(orders: Seq[SortOrder], childOutput:
Seq[NamedExpression]) = {
+ orders.map { order =>
+ val newChild = order.child transformDown { case expr =>
+ val index = childOutput.indexWhere {
+ case Alias(child, _) => child semanticEquals expr
+ case other => other semanticEquals expr
+ }
+ if (index == -1) {
+ expr
+ } else {
+ childOutput(index).toAttribute
+ }
--- End diff --
Would this be simpler as a `find`?
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