STATISTICS

The STATISTICS table provides information about table indexes.

USE information_schema; DESC statistics;
+---------------+---------------+------+------+---------+-------+ | Field | Type | Null | Key | Default | Extra | +---------------+---------------+------+------+---------+-------+ | TABLE_CATALOG | varchar(512) | YES | | NULL | | | TABLE_SCHEMA | varchar(64) | YES | | NULL | | | TABLE_NAME | varchar(64) | YES | | NULL | | | NON_UNIQUE | varchar(1) | YES | | NULL | | | INDEX_SCHEMA | varchar(64) | YES | | NULL | | | INDEX_NAME | varchar(64) | YES | | NULL | | | SEQ_IN_INDEX | bigint(2) | YES | | NULL | | | COLUMN_NAME | varchar(21) | YES | | NULL | | | COLLATION | varchar(1) | YES | | NULL | | | CARDINALITY | bigint(21) | YES | | NULL | | | SUB_PART | bigint(3) | YES | | NULL | | | PACKED | varchar(10) | YES | | NULL | | | NULLABLE | varchar(3) | YES | | NULL | | | INDEX_TYPE | varchar(16) | YES | | NULL | | | COMMENT | varchar(16) | YES | | NULL | | | INDEX_COMMENT | varchar(1024) | YES | | NULL | | | IS_VISIBLE | varchar(3) | YES | | NULL | | | Expression | varchar(64) | YES | | NULL | | +---------------+---------------+------+------+---------+-------+ 18 rows in set (0.00 sec)

Fields in the STATISTICS table are described as follows:

  • TABLE_CATALOG: The name of the catalog to which the table containing the index belongs. This value is always def.
  • TABLE_SCHEMA: The name of the database to which the table containing the index belongs.
  • TABLE_NAME: The name of the table containing the index.
  • NON_UNIQUE: If the index must not contain duplicate values, the value is 0; if duplicate values are allowed in the index, the value is 1.
  • INDEX_SCHEMA: The name of the database to which the index belongs.
  • INDEX_NAME: The name of the index. If the index is the primary key, then the value is always PRIMARY.
  • SEQ_IN_INDEX: The column number in the index, starting from 1.
  • COLUMN_NAME: The column name. See the description of the Expression column.
  • COLLATION: The sorting method of the columns in the index. The value can be A (ascending order), D (descending order) or NULL (unsorted).
  • CARDINALITY: TiDB does not use this field. The field value is always 0.
  • SUB_PART: The prefix of the index. If only part of the prefix of the column is indexed, the value is the number of indexed characters; if the entire column is indexed, the value is NULL.
  • PACKED: TiDB does not use this field. This value is always NULL.
  • NULLABLE: If the column might contain a NULL value, the value is YES; if not, the value is ''.
  • INDEX_TYPE: The type of the index.
  • COMMENT: Other information related to the index.
  • INDEX_COMMENT: Any comment with comment attribute provided for the index when creating the index.
  • IS_VISIBLE: Whether the optimizer can use this index.
  • Expression For the index key of the non-expression part, this value is NULL; for the index key of the expression part, this value is the expression itself. Refer to Expression Index.

The following statements are equivalent:

SELECT * FROM INFORMATION_SCHEMA.STATISTICS WHERE table_name = 'tbl_name' AND table_schema = 'db_name' SHOW INDEX FROM tbl_name FROM db_name

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