system.columns
包含表的列信息。
DESC system.columns;
+--------------------+---------+------+---------+-------+
| Field | Type | Null | Default | Extra |
+--------------------+---------+------+---------+-------+
| name | VARCHAR | NO | | |
| database | VARCHAR | NO | | |
| table | VARCHAR | NO | | |
| type | VARCHAR | NO | | |
| default_kind | VARCHAR | NO | | |
| default_expression | VARCHAR | NO | | |
| is_nullable | BOOLEAN | NO | false | |
| comment | VARCHAR | NO | | |
+--------------------------+----------+---------------------+------------------+-------------------+--------------+--------------------+-------------+---------+
| name | database | table | column_type | data_type | default_kind | default_expression | is_nullable | comment |
+--------------------------+----------+---------------------+------------------+-------------------+--------------+--------------------+-------------+---------+
| id | system | processes | String | VARCHAR | | | NO | |
| type | system | processes | String | VARCHAR | | | NO | |
| host | system | processes | Nullable(String) | VARCHAR | | | YES | |
| user | system | processes | String | VARCHAR | | | NO | |
| command | system | processes | String | VARCHAR | | | NO | |
| database | system | processes | String | VARCHAR | | | NO | |
| extra_info | system | processes | String | VARCHAR | | | NO | |
| memory_usage | system | processes | Int64 | BIGINT | | | NO | |
| data_read_bytes | system | processes | UInt64 | BIGINT UNSIGNED | | | NO | |
| data_write_bytes | system | processes | UInt64 | BIGINT UNSIGNED | | | NO | |
| scan_progress_read_rows | system | processes | UInt64 | BIGINT UNSIGNED | | | NO | |
| scan_progress_read_bytes | system | processes | UInt64 | BIGINT UNSIGNED | | | NO | |
| mysql_connection_id | system | processes | Nullable(UInt32) | INT UNSIGNED | | | YES | |
....
