[SPARK-17712][SQL] Fix invalid pushdown of data-independent filters beneath aggregates

## What changes were proposed in this pull request?

This patch fixes a minor correctness issue impacting the pushdown of filters beneath aggregates. Specifically, if a filter condition references no grouping or aggregate columns (e.g. `WHERE false`) then it would be incorrectly pushed beneath an aggregate.

Intuitively, the only case where you can push a filter beneath an aggregate is when that filter is deterministic and is defined over the grouping columns / expressions, since in that case the filter is acting to exclude entire groups from the query (like a `HAVING` clause). The existing code would only push deterministic filters beneath aggregates when all of the filter's references were grouping columns, but this logic missed the case where a filter has no references. For example, `WHERE false` is deterministic but is independent of the actual data.

This patch fixes this minor bug by adding a new check to ensure that we don't push filters beneath aggregates when those filters don't reference any columns.

## How was this patch tested?

New regression test in FilterPushdownSuite.

Author: Josh Rosen <joshrosen@databricks.com>

Closes #15289 from JoshRosen/SPARK-17712.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala

@@ -710,7 +710,7 @@ object PushDownPredicate extends Rule[LogicalPlan] with PredicateHelper {
 
       val (pushDown, rest) = candidates.partition { cond =>
         val replaced = replaceAlias(cond, aliasMap)
-        replaced.references.subsetOf(aggregate.child.outputSet)
+        cond.references.nonEmpty && replaced.references.subsetOf(aggregate.child.outputSet)
       }
 
       val stayUp = rest ++ containingNonDeterministic

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/FilterPushdownSuite.scala

@@ -687,6 +687,23 @@ class FilterPushdownSuite extends PlanTest {
     comparePlans(optimized, correctAnswer)
   }
 
+  test("SPARK-17712: aggregate: don't push down filters that are data-independent") {
+    val originalQuery = LocalRelation.apply(testRelation.output, Seq.empty)
+      .select('a, 'b)
+      .groupBy('a)(count('a))
+      .where(false)
+
+    val optimized = Optimize.execute(originalQuery.analyze)
+
+    val correctAnswer = testRelation
+      .select('a, 'b)
+      .groupBy('a)(count('a))
+      .where(false)
+      .analyze
+
+    comparePlans(optimized, correctAnswer)
+  }
+
   test("broadcast hint") {
     val originalQuery = BroadcastHint(testRelation)
       .where('a === 2L && 'b + Rand(10).as("rnd") === 3)