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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