In place of an expression

Subqueries that return a single value (unlike a list of values returned by IN subqueries) can be used just about anywhere an expression is allowed in SQL. It can be a column name, a constant, a function, a scalar subquery, or a combination of column names, constants, and functions connected by operators or subqueries.

For example:

=> SELECT c1 FROM t1 WHERE c1 = ANY (SELECT c1 FROM t2) ORDER BY c1;
=> SELECT c1 FROM t1 WHERE COALESCE((t1.c1 > ANY (SELECT c1 FROM t2)), TRUE);
=> SELECT c1 FROM t1 GROUP BY c1 HAVING
     COALESCE((t1.c1 <> ALL (SELECT c1 FROM t2)), TRUE);

Multi-column expressions are also supported:

=> SELECT c1 FROM t1 WHERE (t1.c1, t1.c2) = ALL (SELECT c1, c2 FROM t2);
=> SELECT c1 FROM t1 WHERE (t1.c1, t1.c2) <> ANY (SELECT c1, c2 FROM t2);

Vertica returns an error on queries where more than one row would be returned by any subquery used as an expression:

=> SELECT c1 FROM t1 WHERE c1 = (SELECT c1 FROM t2) ORDER BY c1;
   ERROR:  more than one row returned by a subquery used as an expression

See also

• Subquery restrictions