Github user dongjoon-hyun commented on a diff in the pull request:
https://github.com/apache/spark/pull/14257#discussion_r72182312
--- Diff: sql/hive/src/test/resources/sqlgen/predicate_subquery.sql ---
@@ -1,4 +1,4 @@
-- This file is automatically generated by LogicalPlanToSQLSuite.
select * from t1 b where exists (select * from t1 a)
--------------------------------------------------------------------------------
-SELECT `gen_attr` AS `a` FROM (SELECT `gen_attr` FROM (SELECT `a` AS
`gen_attr` FROM `default`.`t1`) AS gen_subquery_0 WHERE EXISTS(SELECT
`gen_attr` AS `a` FROM ((SELECT `gen_attr` FROM (SELECT `a` AS `gen_attr` FROM
`default`.`t1`) AS gen_subquery_0) AS gen_subquery_1) AS gen_subquery_1)) AS b
+SELECT `gen_attr_0` AS `a` FROM (SELECT `gen_attr_0` FROM (SELECT `a` AS
`gen_attr_0` FROM `default`.`t1`) AS gen_subquery_0 WHERE EXISTS(SELECT
`gen_attr_1` AS `a` FROM ((SELECT `gen_attr_1` FROM (SELECT `a` AS `gen_attr_1`
FROM `default`.`t1`) AS gen_subquery_2) AS gen_subquery_1) AS gen_subquery_1))
AS b
--- End diff --
For this query, I reformatted like the following. Here, `gen_subquery_xxx`s
are generated uniquely. But, `gen_subquery_1` is repeated due to the added
nested subquery alias. Please note that it's not a repetition by duplicated ID
and happens as a direct double nesting. I think it's okay.
```sql
SELECT `gen_attr_0` AS `a`
FROM (SELECT `gen_attr_0`
FROM (SELECT `a` AS `gen_attr_0`
FROM `default`.`t1`
) AS gen_subquery_0
WHERE EXISTS(SELECT `gen_attr_1` AS `a`
FROM ( (SELECT `gen_attr_1`
FROM (SELECT `a` AS `gen_attr_1`
FROM `default`.`t1`
) AS gen_subquery_2
) AS gen_subquery_1
) AS gen_subquery_1
)
) AS b
```
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