SQL subqueries come in several varieties, but as of super commit 7f23f65, we have yet to add support for even the simplest, e.g.,

$ super -version
Version: 7f23f6560

$ super -c "SELECT 1+(SELECT 1);"
parse error at line 1, column 18:
SELECT 1+(SELECT 1);
             === ^ ===

Details

Repro is with super commit 7f23f65. The query shown above is taken from a sqllogictest. The same sqllogictest file contains many other examples of subqueries.

The same query working as expected in Postgres:

$ psql postgres
psql (17.5 (Homebrew))
Type "help" for help.

postgres=# SELECT 1+(SELECT 1);
 ?column? 
----------
        2
(1 row)