AngersZhuuuu edited a comment on issue #25028: [SPARK-28227][SQL] Support 
TRANSFORM with aggregation.
URL: https://github.com/apache/spark/pull/25028#issuecomment-548694667
 
 
   > Here's what I mean:
   > 
   > test query:
   > 
   > ```
   > SELECT TRANSFORM(key, abs(key))
   > USING 'cat'
   > FROM (SELECT DISTINCT key FROM src);
   > ```
   > 
   > The physical plan without this PR (on master):
   > 
   > ```
   > ScriptTransformation [key#7, abs(key#7)], cat, [key#9, value#10], 
HiveScriptIOSchema(List(),List(),Some(org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe),Some(org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe),List((field.delim,
    )),List((field.delim,   
)),Some(org.apache.hadoop.hive.ql.exec.TextRecordReader),Some(org.apache.hadoop.hive.ql.exec.TextRecordWriter),true)
   > +- *(2) HashAggregate(keys=[1#16], functions=[], output=[key#7])
   >    +- Exchange hashpartitioning(1#16, 1), true, [id=#27]
   >       +- *(1) HashAggregate(keys=[1 AS 1#16], functions=[], output=[1#16])
   >          +- *(1) Scan OneRowRelation[]
   > ```
   > 
   > The physical plan with this PR:
   > 
   > ```
   > ScriptTransformation [key#0, abs(key)#9], cat, [key#2, value#3], 
HiveScriptIOSchema(List(),List(),Some(org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe),Some(org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe),List((field.delim,
     )),List((field.delim,   
)),Some(org.apache.hadoop.hive.ql.exec.TextRecordReader),Some(org.apache.hadoop.hive.ql.exec.TextRecordWriter),true)
   > +- *(2) HashAggregate(keys=[1#10], functions=[], output=[key#0, 
abs(key)#9])
   >    +- Exchange hashpartitioning(1#10, 1), true, [id=#21]
   >       +- *(1) HashAggregate(keys=[1 AS 1#10], functions=[], output=[1#10])
   >          +- *(1) Scan OneRowRelation[]
   > ```
   > 
   > Difference:
   > `+- *(2) HashAggregate(keys=[1#16], functions=[], output=[key#7]) `vs
   > `+- *(2) HashAggregate(keys=[1#10], functions=[], output=[key#0, 
abs(key)#9]) `
   
   This right since we now tread transform's child as an entire logical plan. 
It 's final output is two column, it's right.  And transform use it 's out put 
as transform 's input. Reasonable

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