Github user mgaido91 commented on a diff in the pull request:
https://github.com/apache/spark/pull/22518#discussion_r232580202
--- Diff: sql/core/src/test/scala/org/apache/spark/sql/SubquerySuite.scala
---
@@ -1268,4 +1269,16 @@ class SubquerySuite extends QueryTest with
SharedSQLContext {
assert(getNumSortsInQuery(query5) == 1)
}
}
+
+ test("SPARK-25482: Reuse same Subquery in order to execute it only
once") {
+ withTempView("t1", "t2") {
+ sql("create temporary view t1(a int) using parquet")
+ sql("create temporary view t2(b int) using parquet")
+ val plan = sql("select * from t2 where b > (select max(a) from t1)")
--- End diff --
Sure, please can you check the PR description? I think the context is quite
well explained there.
Anyway, as a quick summary: in this case `b > (select max(a) from t1)` is
pushed down as a datasource filter. So we have 2 instances of `b > (select
max(a) from t1)` and the result is not reused. It is not reused because the
copied plan satisfies `==`, so even if `ReuseSubquery` replaces it, then the
change is ignored.
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