8.6. Boolean Type

8.6. Boolean Type

8.6.布尔值

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

PostgreSQL提供标准SQL中的布尔类型：参见表8.19。boolean类型可以有以下几种状态：“true”, “false”和“unknown”，“unknown”表示SQL中的空值。

Valid literal values for the “true” state are:

“true”状态的可用值为：

TRUE

't'

'true'

'y'

'yes'

'on'

'1'

For the “false” state, the following values can be used:

“false”状态的可用值为：

FALSE

'f'

'false'

'n'

'no'

'off'

'0'

Leading or trailing whitespace is ignored, and case does not matter. The key words TRUE and FALSE are the preferred (SQL-compliant) usage.

会忽略首空格或尾空格，且大小写不敏感。当然，最好使用关键词TRUE和FALSE（符合SQL标准）。

Example 8.2 shows that boolean values are output using the letters t and f.

示例8.2显示布尔值输出时使用字母t和f。

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