Github user gatorsmile commented on the pull request:
https://github.com/apache/spark/pull/11427#issuecomment-200524375
Let me post an example here:
```SQL
SELECT sum(b) FROM parquet_t2 group by a, b
```
The current optimized plan is like
```
Aggregate [a#43L,b#44L], [(sum(b#44L),mode=Complete,isDistinct=false) AS
sum(b)#51L]
+- Project [a#43L,b#44L]
+- Relation[a#43L,b#44L,c#45L,d#46L] ParquetFormat part: struct<>, data:
struct<a:bigint,b:bigint,c:bigint,d:bigint>
```
Ideally, we can directly remove the Project.
```
Aggregate [a#43L,b#44L], [(sum(b#44L),mode=Complete,isDistinct=false) AS
sum(b)#51L]
+- Relation[a#43L,b#44L,c#45L,d#46L] ParquetFormat part: struct<>, data:
struct<a:bigint,b:bigint,c:bigint,d:bigint>
```
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