Song Jun created SPARK-27229:
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Summary: GroupBy Placement in Intersect Distinct
Key: SPARK-27229
URL: https://issues.apache.org/jira/browse/SPARK-27229
Project: Spark
Issue Type: Improvement
Components: SQL
Affects Versions: 3.0.0
Reporter: Song Jun
Intersect operator will be replace by Left Semi Join in Optimizer.
for example:
SELECT a1, a2 FROM Tab1 INTERSECT SELECT b1, b2 FROM Tab2
==> SELECT DISTINCT a1, a2 FROM Tab1 LEFT SEMI JOIN Tab2 ON a1<=>b1 AND
a2<=>b2
if Tabe1 and Tab2 are too large, the join will be very slow, we can reduce the
table data before
Join by place groupby operator under join, that is
==>
SELECT a1, a2 FROM
(SELECT a1,a2 FROM Tab1 GROUP BY a1,a2) X
LEFT SEMI JOIN
(SELECT b1,b2 FROM Tab2 GROUP BY b1,b2) Y
ON X.a1<=>Y.b1 AND X.a2<=>Y.b2
then we can have smaller table data when execute join, because group by has
cut lots of
data
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