PostgreSQL/Select Query/NOT

NOT for boolean value

postgres=#
postgres=#
postgres=# CREATE TABLE myTable (isbn text, in_stock boolean);
CREATE TABLE
postgres=#
postgres=# INSERT INTO myTable VALUES ("0385121679", true);
INSERT 0 1
postgres=# INSERT INTO myTable VALUES ("039480001X", "t");
INSERT 0 1
postgres=# INSERT INTO myTable VALUES ("044100590X", "true");
INSERT 0 1
postgres=# INSERT INTO myTable VALUES ("0451198492", false);
INSERT 0 1
postgres=# INSERT INTO myTable VALUES ("0394900014", "0");
INSERT 0 1
postgres=# INSERT INTO myTable VALUES ("0441172717", "1");
INSERT 0 1
postgres=# INSERT INTO myTable VALUES ("0451160916");
INSERT 0 1
postgres=#
postgres=# select * from myTable;
    isbn    | in_stock
------------+----------
 0385121679 | t
 039480001X | t
 044100590X | t
 0451198492 | f
 0394900014 | f
 0441172717 | t
 0451160916 |
(7 rows)
postgres=#
postgres=#
postgres=# SELECT * FROM myTable WHERE NOT in_stock;
    isbn    | in_stock
------------+----------
 0451198492 | f
 0394900014 | f
(2 rows)
postgres=#
postgres=#
postgres=#
postgres=# drop table myTable;
DROP TABLE
postgres=#