# 8.6. 布林型別

PostgreSQL 支援標準 SQL 的布林型別，如 [Table 8-19](#table-8-19-bu-lin-xing-bie-de-zi-liao-xing-tai-miao-shu) 所示。布林型別有幾種狀態: "true"、"false"，和第三種狀態 "unknown"，"unknown" 會用 SQL 的 null 值表示。

#### Table 8-19. 布林型別的資料型態描述

| Name    | Storage Size | Description            |
| ------- | ------------ | ---------------------- |
| boolean | 1 byte       | state of true or false |

以下的字詞都可以代表 "true" 狀態:

| TRUE   |
| ------ |
| 't'    |
| 'true' |
| 'y'    |
| 'yes'  |
| 'on'   |
| '1'    |

"false" 狀態則可以用以下的字詞表示:

| FALSE   |
| ------- |
| 'f'     |
| 'false' |
| 'n'     |
| 'no'    |
| 'off'   |
| '0'     |

開頭和結尾的空白都會被忽略，也不分大小寫。 為了符合 SQL 用法，建議使用關鍵字 "TRUE" 和 "FALSE"。

[Example 8-2](#example-8-2-shi-yong-bu-lin-xing-bie) 使用字母 t 和 f，來顯示布林型別的輸出。

#### Example 8-2. 使用布林型別

```
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
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.postgresql.tw/16/the-sql-language/data-types/boolean-type.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.