{FROM | IN} tbl_name
    [{FROM | IN} db_name]
    [WHERE expr]

SHOW INDEX returns table index information. The format resembles that of the SQLStatistics call in ODBC.

SHOW INDEX returns the following fields:

  • 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.

  • Collation

    How the column is sorted in the index. In MySQL, this can have values A (Ascending) or NULL (Not sorted).

  • Cardinality

    An estimate of the number of unique values in the index. This is updated by running ANALYZE TABLE or 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 number of indexed characters if the column is only partly indexed, NULL if the entire column is indexed.

  • 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.

You can use db_name.tbl_name as an alternative to the tbl_name FROM db_name syntax. These two statements are equivalent:

SHOW INDEX FROM mytable FROM mydb;
SHOW INDEX FROM mydb.mytable;

The WHERE clause can be given to select rows using more general conditions, as discussed in Section 20.27, “Extensions to SHOW Statements”.

You can also list a table's indexes with the mysqlshow -k db_name tbl_name command.

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