wangyum opened a new pull request #31908:
URL: https://github.com/apache/spark/pull/31908
### What changes were proposed in this pull request?
This pr add new rule to removes outer join if it only has distinct on
streamed side. For example:
```scala
spark.range(200L).selectExpr("id AS a").createTempView("t1")
spark.range(300L).selectExpr("id AS b").createTempView("t2")
spark.sql("SELECT DISTINCT a FROM t1 LEFT JOIN t2 ON a = b").explain(true)
```
Before this pr:
```
== Optimized Logical Plan ==
Aggregate [a#2L], [a#2L]
+- Project [a#2L]
+- Join LeftOuter, (a#2L = b#6L)
:- Project [id#0L AS a#2L]
: +- Range (0, 200, step=1, splits=Some(2))
+- Project [id#4L AS b#6L]
+- Range (0, 300, step=1, splits=Some(2))
```
After this pr:
```
== Optimized Logical Plan ==
Aggregate [a#2L], [a#2L]
+- Project [id#0L AS a#2L]
+- Range (0, 200, step=1, splits=Some(2))
```
### Why are the changes needed?
Improve query performance.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
Unit test.
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