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: The estimated number of unique values ​​in the index. To update this value, execute ANALYZE TABLE.
• 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