postgres=#
postgres=# -- The difference between true and 'true'
postgres=#
postgres=# SELECT true AS boolean_t,
postgres-# 'true' AS string_t,
postgres-# false AS boolean_f,
postgres-# 'false' AS string_f;
boolean_t | string_t | boolean_f | string_f
-----------+----------+-----------+----------
t | true | f | false
(1 row)
postgres=#