Unnesting of scalar subqueries in select clause

Nenad Noveljic

The optimizer currently doesn't unnest scalar subqueries in the select clause, even when feasible.

Here's a list of such cases:

https://nenadnoveljic.com/blog/correlated-subqueries-in-the-select-clause/

https://nenadnoveljic.com/blog/correlated-subqueries-in-the-select-clause-2/

Such unnested subqueries must be executed for every row in the driving rowset.