[GitHub] [arrow-datafusion] andygrove commented on issue #3725: Add support for wider range of scalar subqueries in `scalar_subquery_to_join`

[GitBox <gi...@apache.org>]

andygrove commented on issue #3725:
URL: https://github.com/apache/arrow-datafusion/issues/3725#issuecomment-1271593583

   This is going to be harder than I realized. We need to check that scalar subqueries return a single row at some point during execution. I am not sure that we can translate queries to joins if there is the possibility of more than one row being returned.
   
   Postgres example:
   
   ```
   postgres=# select * from test t1 where a = (select distinct b from test where b > 7);
    a | b 
   ---+---
   (0 rows)
   
   postgres=# select * from test t1 where a = (select distinct b from test where b > 3);
   ERROR:  more than one row returned by a subquery used as an expression
   ```


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