Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/7593#discussion_r35803343
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/Analyzer.scala
---
@@ -947,6 +948,63 @@ class Analyzer(
Project(p.output, newPlan.withNewChildren(newChild :: Nil))
}
}
+
+ /**
+ * Removes all still-need-evaluate ordering expressions from sort and
use an inner project to
+ * materialize them, finally use a outer project to project them away to
keep the result same.
+ * Then we can make sure we only sort by [[AttributeReference]]s.
+ *
+ * As an example,
+ * {{{
+ * Sort('a, 'b + 1,
+ * Relation('a, 'b))
+ * }}}
+ * will be turned into:
+ * {{{
+ * Project('a, 'b,
+ * Sort('a, '_sortCondition,
+ * Project('a, 'b, ('b + 1).as("_sortCondition"),
+ * Relation('a, 'b))))
+ * }}}
+ */
+ object RemoveEvaluationFromSort extends Rule[LogicalPlan] {
+ private def hasAlias(expr: Expression) = {
+ expr.find {
+ case a: Alias => true
+ case _ => false
+ }.isDefined
+ }
+
+ override def apply(plan: LogicalPlan): LogicalPlan = plan transform {
+ // The ordering expressions have no effect to the output schema of
`Sort`,
+ // so `Alias`s in ordering expressions are unnecessary and we should
remove them.
+ case s @ Sort(ordering, _, _) if ordering.exists(hasAlias) =>
+ val newOrdering = ordering.map(_.transformUp {
+ case Alias(child, _) => child
+ }.asInstanceOf[SortOrder])
+ s.copy(order = newOrdering)
+
+ case s @ Sort(ordering, global, child)
+ if s.expressions.forall(_.resolved) && s.childrenResolved &&
!s.hasNoEvaluation =>
+
+ val (ref, needEval) =
ordering.partition(_.child.isInstanceOf[AttributeReference])
+
+ val namedExpr = needEval.map(_.child match {
+ case n: NamedExpression => n
+ case e => Alias(e, "_sortCondition")()
+ })
+
+ val newOrdering = ref ++ needEval.zip(namedExpr).map { case
(order, ne) =>
--- End diff --
I think there is a bug here. We need to consider the original ordering of
the expressions or we might sort differently. Consider:
```scala
Seq((1,2,3,4)).toDF("a", "b", "c", "d").registerTempTable("test")
scala> sqlContext.sql("SELECT * FROM test ORDER BY a + 1, b").queryExecution
== Parsed Logical Plan ==
'Sort [('a + 1) ASC,'b ASC], true
'Project [unresolvedalias(*)]
'UnresolvedRelation [test], None
== Optimized Logical Plan ==
Project [a#4,b#5,c#6,d#7]
Sort [b#5 ASC,_sortCondition#9 ASC], true
LocalRelation [a#4,b#5,c#6,d#7,_sortCondition#9], [[1,2,3,4,2]]
```
Notice how we are now sorting by `b` before `a + 1`.
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