Details
Blocker Description
Hey,
We encountered a case where Spark SQL does not seem to handle WHERE .. IN correctly, when used in combination with UNION, but instead returns also rows that do not fulfill the condition. Swapping the order of the datasets in the UNION makes the problem go away. Repro below:
sql = SQLContext(sc)
a = spark.createDataFrame([{'id': 'a', 'num': 2}, {'id':'b', 'num':1}])
b = spark.createDataFrame([{'id': 'a', 'num': 2}, {'id':'b', 'num':1}])
a.registerTempTable('a')
b.registerTempTable('b')
bug = sql.sql("""
SELECT id,num,source FROM
(
SELECT id, num, 'a' as source FROM a
UNION ALL
SELECT id, num, 'b' as source FROM b
) AS c
WHERE c.id IN (SELECT id FROM b WHERE num = 2)
""")
no_bug = sql.sql("""
SELECT id,num,source FROM
(
SELECT id, num, 'b' as source FROM b
UNION ALL
SELECT id, num, 'a' as source FROM a
) AS c
WHERE c.id IN (SELECT id FROM b WHERE num = 2)
""")
bug.show()
no_bug.show()
bug.explain(True)
no_bug.explain(True)
This results in one extra row in the "bug" DF coming from DF "b", that should not be there as it
>>> bug.show() +---+---+------+ | id|num|source| +---+---+------+ | a| 2| a| | a| 2| b| | b| 1| b| +---+---+------+ >>> no_bug.show() +---+---+------+ | id|num|source| +---+---+------+ | a| 2| b| | a| 2| a| +---+---+------+
The reason can be seen in the query plans:
>>> bug.explain(True) ... == Optimized Logical Plan == Union :- Project [id#0, num#1L, a AS source#136] : +- Join LeftSemi, (id#0 = id#4) : :- LogicalRDD [id#0, num#1L], false : +- Project [id#4] : +- Filter (isnotnull(num#5L) && (num#5L = 2)) : +- LogicalRDD [id#4, num#5L], false +- Join LeftSemi, (id#4#172 = id#4#172) :- Project [id#4, num#5L, b AS source#137] : +- LogicalRDD [id#4, num#5L], false +- Project [id#4 AS id#4#172] +- Filter (isnotnull(num#5L) && (num#5L = 2)) +- LogicalRDD [id#4, num#5L], false
Note the line +- Join LeftSemi, (id#4#172 = id#4#172) - this condition seems wrong, and I believe it causes the LeftSemi to return true for all rows in the left-hand-side table, thus failing to filter as the WHERE .. IN should. Compare with the non-buggy version, where both LeftSemi joins have distinct #-things on both sides:
>>> no_bug.explain() ... == Optimized Logical Plan == Union :- Project [id#4, num#5L, b AS source#142] : +- Join LeftSemi, (id#4 = id#4#173) : :- LogicalRDD [id#4, num#5L], false : +- Project [id#4 AS id#4#173] : +- Filter (isnotnull(num#5L) && (num#5L = 2)) : +- LogicalRDD [id#4, num#5L], false +- Project [id#0, num#1L, a AS source#143] +- Join LeftSemi, (id#0 = id#4#173) :- LogicalRDD [id#0, num#1L], false +- Project [id#4 AS id#4#173] +- Filter (isnotnull(num#5L) && (num#5L = 2)) +- LogicalRDD [id#4, num#5L], false
Best,
-Arttu
