Boolean

The valid text values for "true" are TRUE, t, true, and 1.

The valid text values for the "false" value are FALSE, f, false, and 0.

TRUE and FALSE are standard usages (SQL-compatible).

Example:

select BOOLEAN '0';
 _col0 
-------
 false 
(1 row)
 
select BOOLEAN 'TRUE';
 _col0 
-------
 true  
(1 row)
 
select BOOLEAN 't';
 _col0 
-------
 true  
(1 row)