MySQL :: MySQL 8.4 参考手册 :: 28.8 SHOW 语句的扩展

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MySQL 8.4 参考手册 / INFORMATION_SCHEMA 表 / SHOW 语句的扩展

28.8 SHOW 语句的扩展

一些对 SHOW 语句的扩展伴随着 INFORMATION_SCHEMA 的实现。

SHOW 可用于获取有关 INFORMATION_SCHEMA 本身结构的信息。
一些 SHOW 语句接受 WHERE 子句，该子句在指定要显示哪些行方面提供了更大的灵活性。

INFORMATION_SCHEMA 是一个信息数据库，因此它的名称包含在 SHOW DATABASES 的输出中。类似地，SHOW TABLES 可以与 INFORMATION_SCHEMA 一起使用以获取其表的列表。

mysql> SHOW TABLES FROM INFORMATION_SCHEMA;
+---------------------------------------+
| Tables_in_INFORMATION_SCHEMA          |
+---------------------------------------+
| CHARACTER_SETS                        |
| COLLATIONS                            |
| COLLATION_CHARACTER_SET_APPLICABILITY |
| COLUMNS                               |
| COLUMN_PRIVILEGES                     |
| ENGINES                               |
| EVENTS                                |
| FILES                                 |
| KEY_COLUMN_USAGE                      |
| PARTITIONS                            |
| PLUGINS                               |
| PROCESSLIST                           |
| REFERENTIAL_CONSTRAINTS               |
| ROUTINES                              |
| SCHEMATA                              |
| SCHEMA_PRIVILEGES                     |
| STATISTICS                            |
| TABLES                                |
| TABLE_CONSTRAINTS                     |
| TABLE_PRIVILEGES                      |
| TRIGGERS                              |
| USER_PRIVILEGES                       |
| VIEWS                                 |
+---------------------------------------+

SHOW COLUMNS 和 DESCRIBE 可以显示有关各个 INFORMATION_SCHEMA 表中列的信息。

接受 LIKE 子句以限制显示行的 SHOW 语句也允许使用 WHERE 子句来指定所选行必须满足的更一般的条件。

SHOW CHARACTER SET
SHOW COLLATION
SHOW COLUMNS
SHOW DATABASES
SHOW FUNCTION STATUS
SHOW INDEX
SHOW OPEN TABLES
SHOW PROCEDURE STATUS
SHOW STATUS
SHOW TABLE STATUS
SHOW TABLES
SHOW TRIGGERS
SHOW VARIABLES

WHERE 子句（如果存在）将针对 SHOW 语句显示的列名进行评估。例如，SHOW CHARACTER SET 语句生成以下输出列：

mysql> SHOW CHARACTER SET;
+----------+-----------------------------+---------------------+--------+
| Charset  | Description                 | Default collation   | Maxlen |
+----------+-----------------------------+---------------------+--------+
| big5     | Big5 Traditional Chinese    | big5_chinese_ci     |      2 |
| dec8     | DEC West European           | dec8_swedish_ci     |      1 |
| cp850    | DOS West European           | cp850_general_ci    |      1 |
| hp8      | HP West European            | hp8_english_ci      |      1 |
| koi8r    | KOI8-R Relcom Russian       | koi8r_general_ci    |      1 |
| latin1   | cp1252 West European        | latin1_swedish_ci   |      1 |
| latin2   | ISO 8859-2 Central European | latin2_general_ci   |      1 |
...

要将 WHERE 子句与 SHOW CHARACTER SET 一起使用，您需要引用这些列名。例如，以下语句显示有关默认排序规则包含字符串 'japanese' 的字符集的信息：

mysql> SHOW CHARACTER SET WHERE `Default collation` LIKE '%japanese%';
+---------+---------------------------+---------------------+--------+
| Charset | Description               | Default collation   | Maxlen |
+---------+---------------------------+---------------------+--------+
| ujis    | EUC-JP Japanese           | ujis_japanese_ci    |      3 |
| sjis    | Shift-JIS Japanese        | sjis_japanese_ci    |      2 |
| cp932   | SJIS for Windows Japanese | cp932_japanese_ci   |      2 |
| eucjpms | UJIS for Windows Japanese | eucjpms_japanese_ci |      3 |
+---------+---------------------------+---------------------+--------+

此语句显示多字节字符集：

mysql> SHOW CHARACTER SET WHERE Maxlen > 1;
+---------+---------------------------------+---------------------+--------+
| Charset | Description                     | Default collation   | Maxlen |
+---------+---------------------------------+---------------------+--------+
| big5    | Big5 Traditional Chinese        | big5_chinese_ci     |      2 |
| cp932   | SJIS for Windows Japanese       | cp932_japanese_ci   |      2 |
| eucjpms | UJIS for Windows Japanese       | eucjpms_japanese_ci |      3 |
| euckr   | EUC-KR Korean                   | euckr_korean_ci     |      2 |
| gb18030 | China National Standard GB18030 | gb18030_chinese_ci  |      4 |
| gb2312  | GB2312 Simplified Chinese       | gb2312_chinese_ci   |      2 |
| gbk     | GBK Simplified Chinese          | gbk_chinese_ci      |      2 |
| sjis    | Shift-JIS Japanese              | sjis_japanese_ci    |      2 |
| ucs2    | UCS-2 Unicode                   | ucs2_general_ci     |      2 |
| ujis    | EUC-JP Japanese                 | ujis_japanese_ci    |      3 |
| utf16   | UTF-16 Unicode                  | utf16_general_ci    |      4 |
| utf16le | UTF-16LE Unicode                | utf16le_general_ci  |      4 |
| utf32   | UTF-32 Unicode                  | utf32_general_ci    |      4 |
| utf8mb3 | UTF-8 Unicode                   | utf8mb3_general_ci  |      3 |
| utf8mb4 | UTF-8 Unicode                   | utf8mb4_0900_ai_ci  |      4 |
+---------+---------------------------------+---------------------+--------+