Postgres supports bool as the SQL3 boolean type. bool can have one of only two states: 'true' or 'false'. A third state, 'unknown', is not implemented and is not suggested in SQL3; NULL is an effective substitute. bool can be used in any boolean expression, and boolean expressions always evaluate to a result compatible with this type.
bool uses 4 bytes of storage.
Table 8-12. Postgres Boolean Type
| State | Output | Input |
|---|---|---|
| True | 't' | TRUE, 't', 'true', 'y', 'yes', '1' |
| False | 'f' | FALSE, 'f', 'false', 'n', 'no', '0' |