PostgreSQL 7.2.1 Documentation
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3.6. Boolean Type

PostgreSQL provides the SQL99 type boolean. boolean can have one of only two states: "true" or "false". A third state, "unknown", is represented by the SQL NULL state.

Valid literal values for the "true" state are:

TRUE
't'
'true'
'y'
'yes'
'1'

For the "false" state, the following values can be used:

FALSE
'f'
'false'
'n'
'no'
'0'

Using the key words TRUE and FALSE is preferred (and SQL-compliant).

Example 3-2. Using the boolean type

CREATE TABLE test1 (a boolean, b text);
INSERT INTO test1 VALUES (TRUE, 'sic est');
INSERT INTO test1 VALUES (FALSE, 'non est');
SELECT * FROM test1;
 a |    b
---+---------
 t | sic est
 f | non est

SELECT * FROM test1 WHERE a;
 a |    b
---+---------
 t | sic est

Example 3-2 shows that boolean values are output using the letters t and f.

Tip: Values of the boolean type cannot be cast directly to other types (e.g., CAST (boolval AS integer) does not work). This can be accomplished using the CASE expression: CASE WHEN boolval THEN 'value if true' ELSE 'value if false' END. See also Section 4.12.

boolean uses 1 byte of storage.

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