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8.6. Boolean Type

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

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 8-2. 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 8-2 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 9.12.

boolean uses 1 byte of storage.

Comments


April 1, 2004, 5:34 p.m.

If you work on compatibility issues with MySQL, note that PostgreSQL understand bool as an abbreviation of boolean. This makes it work on MySQL as well (it knows only bool and silently converts to tinyint(1)).

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