TABLES

The TABLES table provides information about tables in databases:

USE information_schema; DESC tables;
+---------------------------+---------------+------+------+----------+-------+ | Field | Type | Null | Key | Default | Extra | +---------------------------+---------------+------+------+----------+-------+ | TABLE_CATALOG | varchar(512) | YES | | NULL | | | TABLE_SCHEMA | varchar(64) | YES | | NULL | | | TABLE_NAME | varchar(64) | YES | | NULL | | | TABLE_TYPE | varchar(64) | YES | | NULL | | | ENGINE | varchar(64) | YES | | NULL | | | VERSION | bigint(21) | YES | | NULL | | | ROW_FORMAT | varchar(10) | YES | | NULL | | | TABLE_ROWS | bigint(21) | YES | | NULL | | | AVG_ROW_LENGTH | bigint(21) | YES | | NULL | | | DATA_LENGTH | bigint(21) | YES | | NULL | | | MAX_DATA_LENGTH | bigint(21) | YES | | NULL | | | INDEX_LENGTH | bigint(21) | YES | | NULL | | | DATA_FREE | bigint(21) | YES | | NULL | | | AUTO_INCREMENT | bigint(21) | YES | | NULL | | | CREATE_TIME | datetime | YES | | NULL | | | UPDATE_TIME | datetime | YES | | NULL | | | CHECK_TIME | datetime | YES | | NULL | | | TABLE_COLLATION | varchar(32) | NO | | utf8_bin | | | CHECKSUM | bigint(21) | YES | | NULL | | | CREATE_OPTIONS | varchar(255) | YES | | NULL | | | TABLE_COMMENT | varchar(2048) | YES | | NULL | | | TIDB_TABLE_ID | bigint(21) | YES | | NULL | | | TIDB_ROW_ID_SHARDING_INFO | varchar(255) | YES | | NULL | | +---------------------------+---------------+------+------+----------+-------+ 23 rows in set (0.00 sec)
SELECT * FROM tables WHERE table_schema='mysql' AND table_name='user'\G
*************************** 1. row *************************** TABLE_CATALOG: def TABLE_SCHEMA: mysql TABLE_NAME: user TABLE_TYPE: BASE TABLE ENGINE: InnoDB VERSION: 10 ROW_FORMAT: Compact TABLE_ROWS: 0 AVG_ROW_LENGTH: 0 DATA_LENGTH: 0 MAX_DATA_LENGTH: 0 INDEX_LENGTH: 0 DATA_FREE: 0 AUTO_INCREMENT: NULL CREATE_TIME: 2020-07-05 09:25:51 UPDATE_TIME: NULL CHECK_TIME: NULL TABLE_COLLATION: utf8mb4_bin CHECKSUM: NULL CREATE_OPTIONS: TABLE_COMMENT: TIDB_TABLE_ID: 5 TIDB_ROW_ID_SHARDING_INFO: NULL 1 row in set (0.00 sec)

The following statements are equivalent:

SELECT table_name FROM INFORMATION_SCHEMA.TABLES WHERE table_schema = 'db_name' [AND table_name LIKE 'wild'] SHOW TABLES FROM db_name [LIKE 'wild']

The description of columns in the TABLES table is as follows:

  • TABLE_CATALOG: The name of the catalog which the table belongs to. The value is always def.
  • TABLE_SCHEMA: The name of the schema which the table belongs to.
  • TABLE_NAME: The name of the table.
  • TABLE_TYPE: The type of the table.
  • ENGINE: The type of the storage engine. The value is currently InnoDB.
  • VERSION: Version. The value is 10 by default.
  • ROW_FORMAT: The row format. The value is currently Compact.
  • TABLE_ROWS: The number of rows in the table in statistics.
  • AVG_ROW_LENGTH: The average row length of the table. AVG_ROW_LENGTH = DATA_LENGTH / TABLE_ROWS.
  • DATA_LENGTH: Data length. DATA_LENGTH = TABLE_ROWS * the sum of storage lengths of the columns in the tuple. The replicas of TiKV are not taken into account.
  • MAX_DATA_LENGTH: The maximum data length. The value is currently 0, which means the data length has no upper limit.
  • INDEX_LENGTH: The index length. INDEX_LENGTH = TABLE_ROWS * the sum of lengths of the columns in the index tuple. The replicas of TiKV are not taken into account.
  • DATA_FREE: Data fragment. The value is currently 0.
  • AUTO_INCREMENT: The current step of the auto- increment primary key.
  • CREATE_TIME: The time at which the table is created.
  • UPDATE_TIME: The time at which the table is updated.
  • CHECK_TIME: The time at which the table is checked.
  • TABLE_COLLATION: The collation of strings in the table.
  • CHECKSUM: Checksum.
  • CREATE_OPTIONS: Creates options.
  • TABLE_COMMENT: The comments and notes of the table.

Most of the information in the table is the same as MySQL. Only two columns are newly defined by TiDB:

  • TIDB_TABLE_ID: to indicate the internal ID of a table. This ID is unique in a TiDB cluster.
  • TIDB_ROW_ID_SHARDING_INFO: to indicate the sharding type of a table. The possible values are as follows:
    • "NOT_SHARDED": the table is not sharded.
    • "NOT_SHARDED(PK_IS_HANDLE)": the table that defines an integer Primary Key as its row id is not sharded.
    • "PK_AUTO_RANDOM_BITS={bit_number}": the table that defines an integer Primary Key as its row id is sharded because the Primary Key is assigned with AUTO_RANDOM attribute.
    • "SHARD_BITS={bit_number}": the table is sharded using SHARD_ROW_ID_BITS={bit_number}.
    • NULL: the table is a system table or view, and thus cannot be sharded.

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