SHOW INDEX Syntax

SHOW INDEX returns table index information. The format resembles that of the SQLStatistics call in ODBC. This statement requires some privilege for any column in the table.

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 MariaDB 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. If not, the column contains NO.

  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.

• Index_comment

  Any comment provided for the index with a COMMENT attribute when the index was created.

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;

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

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