Description
This issue adds a new logical optimizer, `PropagateEmptyRelation`, to collapse a logical plans consisting of only empty LocalRelations.
*Optimizer Targets*
1. Binary(or Higher)-node Logical Plans
- Union with all empty children.
- Join with one or two empty children (including Intersect/Except).
2. Unary-node Logical Plans - Project/Filter/Sample/Join/Limit/Repartition with all empty children.
- Aggregate with all empty children and without AggregateFunction expressions, COUNT.
- Generate with Explode because other UserDefinedGenerators like Hive UDTF returns results.
*Sample Query*
WITH t1 AS (SELECT a FROM VALUES 1 t(a)),
t2 AS (SELECT b FROM VALUES 1 t(b) WHERE 1=2)
SELECT a,b
FROM t1, t2
WHERE a=b
GROUP BY a,b
HAVING a>1
ORDER BY a,b
*Before*
scala> sql("with t1 as (select a from values 1 t(a)), t2 as (select b from values 1 t(b) where 1=2) select a,b from t1, t2 where a=b group by a,b having a>1 order by a,b").explain == Physical Plan == *Sort [a#0 ASC, b#1 ASC], true, 0 +- Exchange rangepartitioning(a#0 ASC, b#1 ASC, 200) +- *HashAggregate(keys=[a#0, b#1], functions=[]) +- Exchange hashpartitioning(a#0, b#1, 200) +- *HashAggregate(keys=[a#0, b#1], functions=[]) +- *BroadcastHashJoin [a#0], [b#1], Inner, BuildRight :- *Filter (isnotnull(a#0) && (a#0 > 1)) : +- LocalTableScan [a#0] +- BroadcastExchange HashedRelationBroadcastMode(List(cast(input[0, int, false] as bigint))) +- *Filter (isnotnull(b#1) && (b#1 > 1)) +- LocalTableScan <empty>, [b#1]
*After*
scala> sql("with t1 as (select a from values 1 t(a)), t2 as (select b from values 1 t(b) where 1=2) select a,b from t1, t2 where a=b group by a,b having a>1 order by a,b").explain
== Physical Plan ==
LocalTableScan <empty>, [a#0, b#1]
Attachments
Issue Links
- is related to
-
SPARK-20686 PropagateEmptyRelation incorrectly handles aggregate without grouping expressions
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- Resolved
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- links to
