character_sets

character_sets视图提供有关可用字符集的信息。该视图为只读，不允许修改。所有用户对这个视图有“读取”权限。

GUC参数m_format_dev_version控制行为保持前向兼容，当m_format_dev_version取值为s2时，可使用最新功能，其他取值时保持前向兼容。

当m_format_dev_version取值不为s2时，视图仅展示当前数据库的字符集信息：

m_db=# SET m_format_dev_version=s1;
SET
m_db=# SELECT * FROM information_schema.character_sets;
 CHARACTER_SET_NAME | DEFAULT_COLLATE_NAME |         DESCRIPTION          | MAXLEN
--------------------+----------------------+------------------------------+--------
 UTF8               | utf8mb4_general_ci   | utf8mb4_general_ci collation |      4
(1 row)

m_format_dev_version取值为s2时，视图可以查询所有可用字符集信息：

m_db=# SET m_format_dev_version=s2;
SET
m_db=# SELECT * FROM information_schema.character_sets;
 CHARACTER_SET_NAME | DEFAULT_COLLATE_NAME |         DESCRIPTION          | MAXLEN
--------------------+----------------------+------------------------------+--------
 binary             | binary               | binary collation             |      1
 gbk                | gbk_chinese_ci       | gbk_chinese_ci collation     |      2
 utf8mb4            | utf8mb4_general_ci   | utf8mb4_general_ci collation |      4
 gb18030            | gb18030_chinese_ci   | gb18030_chinese_ci collation |      4
 latin1             | latin1_swedish_ci    | latin1_swedish_ci collation  |      1
(5 rows)