PostgreSQL

PostgreSQL Elephant Logo

8.6. Boolean Type #

PostgreSQL provides the standard SQL type boolean; see Table 8.19. The boolean type can have several states: “[.quote]#true, [.quote]false, and a third state, [.quote]unknown”#, which is represented by the SQL null value.

Table 8.19. Boolean Data Type

Name Storage Size Description

boolean

1 byte

state of true or false

+

Boolean constants can be represented in SQL queries by the SQL key words TRUE, FALSE, and NULL.

The datatype input function for type boolean accepts these string representations for the “[.quote]#true”# state:

true

yes

on

1

and these representations for the “[.quote]#false”# state:

false

no

off

0

Unique prefixes of these strings are also accepted, for example t or n. Leading or trailing whitespace is ignored, and case does not matter.

The datatype output function for type boolean always emits either t or f, as shown in Example 8.2.

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
+

The key words TRUE and FALSE are the preferred (SQL-compliant) method for writing Boolean constants in SQL queries. But you can also use the string representations by following the generic string-literal constant syntax described in Section 4.1.2.7, for example 'yes'::boolean.

Note that the parser automatically understands that TRUE and FALSE are of type boolean, but this is not so for NULL because that can have any type. So in some contexts you might have to cast NULL to boolean explicitly, for example NULL::boolean. Conversely, the cast can be omitted from a string-literal Boolean value in contexts where the parser can deduce that the literal must be of type boolean.


Prev Up Next

8.5. Date/Time Types

Home

8.7. Enumerated Types

Submit correction

If you see anything in the documentation that is not correct, does not match your experience with the particular feature or requires further clarification, please use this form to report a documentation issue.

Copyright © 1996-2024 The PostgreSQL Global Development Group