wangyum opened a new pull request #33590:
URL: https://github.com/apache/spark/pull/33590
### What changes were proposed in this pull request?
`Coalesce` returns the first expression if it is non nullable. For example:
```scala
sql("create table t1(a string, b string) using parquet")
sql("select a, Coalesce(count(b), 0) from t1 group by a").explain(true)
```
Before this pr:
```
== Optimized Logical Plan ==
Aggregate [a#0], [a#0, coalesce(count(b#1), 0) AS coalesce(count(b), 0)#3L]
+- Relation default.t1[a#0,b#1] parquet
```
After this pr:
```
== Optimized Logical Plan ==
Aggregate [a#0], [a#0, count(b#1) AS coalesce(count(b), 0)#3L]
+- Relation default.t1[a#0,b#1] parquet
```
### 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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