SHOW INDEX statement is used to check the indexes created by a UNIQUE constraint on a MySQL table.
Syntax
SHOW INDEX from table_name;
Example
Suppose we have the table ‘empl’ which have a UNIQUE constraint on column ‘empno’.
mysql> describe empl; +--------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +--------+-------------+------+-----+---------+-------+ | empno | int(11) | YES | UNI | NULL | | | F_name | varchar(20) | YES | | NULL | | +--------+-------------+------+-----+---------+-------+ 2 rows in set (0.23 sec)
Now as we know that UNIQUE constraint creates indexes which can be checked form the following query −
mysql> Show Index from empl\G *************************** 1. row *************************** Table: empl Non_unique: 0 Key_name: empno Seq_in_index: 1 Column_name: empno Collation: A Cardinality: 0 Sub_part: NULL Packed: NULL Null: YES Index_type: BTREE Comment: Index_comment: 1 row in set (0.02 sec)
The ‘key_name’ in the above result set shows the name of the index and ‘column_name’ is the name of the column on which this index has been added.