Boolean values are typically the TRUE and FALSE constants.
TRUE is evaluated to 1 and FALSE is evaluated to 0. The constant names are case-insensitive.
obclient> SELECT TRUE, true, FALSE, false;
+------+------+-------+-------+
TRUE true FALSE false
+------+------+-------+-------+
1 1 0 0
+------+------+-------+-------+
1 row in set (0.00 sec)