STATISTICS

The STATISTICS table provides information about table indexes.

  1. USE information_schema;
  2. DESC statistics;
  1. +---------------+---------------+------+------+---------+-------+
  2. | Field         | Type          | Null | Key  | Default | Extra |
  3. +---------------+---------------+------+------+---------+-------+
  4. | TABLE_CATALOG | varchar(512)  | YES  |      | NULL    |       |
  5. | TABLE_SCHEMA  | varchar(64)   | YES  |      | NULL    |       |
  6. | TABLE_NAME    | varchar(64)   | YES  |      | NULL    |       |
  7. | NON_UNIQUE    | varchar(1)    | YES  |      | NULL    |       |
  8. | INDEX_SCHEMA  | varchar(64)   | YES  |      | NULL    |       |
  9. | INDEX_NAME    | varchar(64)   | YES  |      | NULL    |       |
  10. | SEQ_IN_INDEX  | bigint(2)     | YES  |      | NULL    |       |
  11. | COLUMN_NAME   | varchar(21)   | YES  |      | NULL    |       |
  12. | COLLATION     | varchar(1)    | YES  |      | NULL    |       |
  13. | CARDINALITY   | bigint(21)    | YES  |      | NULL    |       |
  14. | SUB_PART      | bigint(3)     | YES  |      | NULL    |       |
  15. | PACKED        | varchar(10)   | YES  |      | NULL    |       |
  16. | NULLABLE      | varchar(3)    | YES  |      | NULL    |       |
  17. | INDEX_TYPE    | varchar(16)   | YES  |      | NULL    |       |
  18. | COMMENT       | varchar(16)   | YES  |      | NULL    |       |
  19. | INDEX_COMMENT | varchar(1024) | YES  |      | NULL    |       |
  20. | IS_VISIBLE    | varchar(3)    | YES  |      | NULL    |       |
  21. | Expression    | varchar(64)   | YES  |      | NULL    |       |
  22. +---------------+---------------+------+------+---------+-------+
  23. 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:

  1. SELECT * FROM INFORMATION_SCHEMA.STATISTICS
  2.   WHERE table_name = 'tbl_name'
  3.   AND table_schema = 'db_name'
  5. SHOW INDEX
  6.   FROM tbl_name
  7.   FROM db_name