[jira] [Created] (FLINK-6101) GroupBy fields with expression can not be selected either using original name or expression

[Shang Yuanchun (Jira)]

lincoln.lee created FLINK-6101:
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             Summary: GroupBy fields with expression can not be selected either using original name or expression
                 Key: FLINK-6101
                 URL: https://issues.apache.org/jira/browse/FLINK-6101
             Project: Flink
          Issue Type: Bug
          Components: Table API & SQL
            Reporter: lincoln.lee


currently the TableAPI do not support selecting GroupBy fields with expression either using original field name or the expression

```
 val t = CollectionDataSets.get5TupleDataSet(env).toTable(tEnv, 'a, 'b, 'c, 'd, 'e)
        .groupBy('e, 'b % 3)
        .select('b, 'c.min, 'e, 'a.avg, 'd.count)
```
cause
```
 val t = CollectionDataSets.get5TupleDataSet(env).toTable(tEnv, 'a, 'b, 'c, 'd, 'e)
        .groupBy('e, 'b % 3)
        .select('b, 'c.min, 'e, 'a.avg, 'd.count)
```
and

```
 val t = CollectionDataSets.get5TupleDataSet(env).toTable(tEnv, 'a, 'b, 'c, 'd, 'e)
        .groupBy('e, 'b % 3)
        .select('b%3, 'c.min, 'e, 'a.avg, 'd.count)
```
will cause

```
org.apache.flink.table.api.ValidationException: Cannot resolve [b] given input [e, ('b % 3), TMP_0, TMP_1, TMP_2].
```

and add an alias "group(e, 'b%3 as 'b)" still doesn't work
```
java.lang.IllegalArgumentException: field [b] not found; input fields are: [e, b5, TMP_0, TMP_1, TMP_2]
```

the only way to get this work can be
```
 val t = CollectionDataSets.get5TupleDataSet(env).toTable(tEnv, 'a, 'b, 'c, 'd, 'e)
        .select('a, 'b%3 as 'b, 'c, 'd, 'e)
        .groupBy('e, 'b)
        .select('b, 'c.min, 'e, 'a.avg, 'd.count)
```

I'm confused, should we add support alias in groupBy clause? ( it seems a bit odd against SQL, but TableAPI has a different groupBy grammar )






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