system.columns
包含有关表列的信息。
DESC system.columns;
+--------------------+---------+------+---------+-------+
| 字段 | 类型 | 空值 | 默认值 | 额外 |
+--------------------+---------+------+---------+-------+
| name | VARCHAR | 否 | | |
| database | VARCHAR | 否 | | |
| table | VARCHAR | 否 | | |
| type | VARCHAR | 否 | | |
| default_kind | VARCHAR | 否 | | |
| default_expression | VARCHAR | 否 | | |
| is_nullable | BOOLEAN | 否 | false | |
| comment | VARCHAR | 否 | | |
+--------------------------+----------+---------------------+------------------+-------------------+--------------+--------------------+-------------+---------+
| 名称 | 数据库 | 表 | 列类型 | 数据类型 | 默认类型 | 默认表达式 | 可为空 | 注释 |
+--------------------------+----------+---------------------+------------------+-------------------+--------------+--------------------+-------------+---------+
| id | system | processes | String | VARCHAR | | | 否 | |
| type | system | processes | String | VARCHAR | | | 否 | |
| host | system | processes | Nullable(String) | VARCHAR | | | 是 | |
| user | system | processes | String | VARCHAR | | | 否 | |
| command | system | processes | String | VARCHAR | | | 否 | |
| database | system | processes | String | VARCHAR | | | 否 | |
| extra_info | system | processes | String | VARCHAR | | | 否 | |
| memory_usage | system | processes | Int64 | BIGINT | | | 否 | |
| data_read_bytes | system | processes | UInt64 | BIGINT UNSIGNED | | | 否 | |
| data_write_bytes | system | processes | UInt64 | BIGINT UNSIGNED | | | 否 | |
| scan_progress_read_rows | system | processes | UInt64 | BIGINT UNSIGNED | | | 否 | |
| scan_progress_read_bytes | system | processes | UInt64 | BIGINT UNSIGNED | | | 否 | |
| mysql_connection_id | system | processes | Nullable(UInt32) | INT UNSIGNED | | | 是 | |
....
