SHOW INDEX

语法说明

SHOW INDEX returns table index information.

SHOW INDEX returns the following fields:

Fields	Description
Table	The name of the table.
Non_unique	0 if the index cannot contain duplicates, 1 if it can.
Key_name	The name of the index. If the index is the primary key, the name is always PRIMARY.
Seq_in_index	The column sequence number in the index, starting with 1.
Column_name	The column name. See also the description for the Expression column.
Collation	How the column is sorted in the index. This can have values A (ascending), D (descending), or NULL (not sorted).
Cardinality	An estimate of the number of unique values in the index. To update this number, run ANALYZE TABLE or (for MyISAM tables) myisamchk -a. Cardinality is counted based on statistics stored as integers, so the value is not necessarily exact even for small tables. The higher the cardinality, the greater the chance that MySQL uses the index when doing joins.
Sub_part	The index prefix. That is, the number of indexed characters if the column is only partly indexed, NULL if the entire column is indexed. Note: Prefix limits are measured in bytes. However, prefix lengths for index specifications in CREATE TABLE, ALTER TABLE, and CREATE INDEX statements are interpreted as number of characters for nonbinary string types (CHAR, VARCHAR, TEXT) and number of bytes for binary string types (BINARY, VARBINARY, BLOB). Take this into account when specifying a prefix length for a nonbinary string column that uses a multibyte character set.
Packed	Indicates how the key is packed. NULL if it is not.
Null	Contains YES if the column may contain NULL values and '' if not.
Index_type	The index method used (BTREE, FULLTEXT, HASH, RTREE).
Comment	Information about the index not described in its own column, such as disabled if the index is disabled.
Visible	Whether the index is visible to the optimizer.
Expression	For a nonfunctional key part, Column_name indicates the column indexed by the key part and Expression is NULL. For a functional key part, Column_name column is NULL and Expression indicates the expression for the key part.

语法结构

> SHOW {INDEX | INDEXES}
    {FROM | IN} tbl_name
    [{FROM | IN} db_name]

Explanations

An alternative to tbl_name FROM db_name syntax is db_name.tbl_name.

示例

CREATE TABLE show_01(sname varchar(30),id int);
mysql> show INDEX FROM show_01;
+---------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+------------------+---------+------------+
| Table   | Non_unique | Key_name   | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment          | Visible | Expression |
+---------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+------------------+---------+------------+
| show_01 |          0 | id         |            1 | id          | A         |           0 | NULL     | NULL   | YES  |            |                  | YES     | NULL       |
| show_01 |          0 | sname      |            1 | sname       | A         |           0 | NULL     | NULL   | YES  |            |                  | YES     | NULL       |
| show_01 |          0 | __mo_rowid |            1 | __mo_rowid  | A         |           0 | NULL     | NULL   | NO   |            | Physical address | NO      | NULL       |
+---------+------------+------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+------------------+---------+------------+
3 rows in set (0.02 sec)