SHOW INDEX

Complete SHOW INDEX reference: SHOW {INDEX|INDEXES|KEYS} FROM tbl_name syntax, output fields (Key_name, Seq_in_index, Cardinality), and WHERE/LIKE filters.

Syntax

SHOW {INDEX | INDEXES | KEYS} 
 FROM tbl_name [FROM db_name]
 [WHERE expr]

Description

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

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

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

SHOW KEYS and SHOW INDEXES are synonyms for SHOW INDEX.

You can also list a table's indexes with the mariadb-show command:

mariadb-show -k db_name tbl_name

The information_schema.STATISTICS table stores similar information.

The following fields are returned by SHOW INDEX.

Field	Description
Table	Table name
Non_unique	1 if the index permits duplicate values, 0 if values must be unique.
Key_name	Index name. The primary key is always named PRIMARY.
Seq_in_index	The column's sequence in the index, beginning with 1.
Column_name	Column name.
Collation	Either A, if the column is sorted in ascending order in the index, or NULL if it's not sorted.
Cardinality	Estimated number of unique values in the index. The cardinality statistics are calculated at various times, and can help the optimizer make improved decisions.
Sub_part	NULL if the entire column is included in the index, or the number of included characters if not.
Packed	NULL if the index is not packed, otherwise how the index is packed.
Null	NULL if NULL values are permitted in the column, an empty string if NULLs are not permitted.
Index_type	The index type, which can be BTREE, FULLTEXT, HASH or RTREE. See Storage Engine Index Types.
Comment	Other information, such as whether the index is disabled.
Index_comment	Contents of the COMMENT attribute when the index was created.
Ignored	Whether or not an index will be ignored by the optimizer. See Ignored Indexes. From MariaDB 10.6.0.

The WHERE and LIKE clauses can be given to select rows using more general conditions, as discussed in Extended SHOW.

Examples

CREATE TABLE IF NOT EXISTS `employees_example` (
  `id` INT(11) NOT NULL AUTO_INCREMENT,
  `first_name` VARCHAR(30) NOT NULL,
  `last_name` VARCHAR(40) NOT NULL,
  `position` VARCHAR(25) NOT NULL,
  `home_address` VARCHAR(50) NOT NULL,
  `home_phone` VARCHAR(12) NOT NULL,
  `employee_code` VARCHAR(25) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `employee_code` (`employee_code`),
  KEY `first_name` (`first_name`,`last_name`)
) ENGINE=Aria;

INSERT INTO `employees_example` (`first_name`, `last_name`, `position`, `home_address`, `home_phone`, `employee_code`)
  VALUES
  ('Mustapha', 'Mond', 'Chief Executive Officer', '692 Promiscuous Plaza', '326-555-3492', 'MM1'),
  ('Henry', 'Foster', 'Store Manager', '314 Savage Circle', '326-555-3847', 'HF1'),
  ('Bernard', 'Marx', 'Cashier', '1240 Ambient Avenue', '326-555-8456', 'BM1'),
  ('Lenina', 'Crowne', 'Cashier', '281 Bumblepuppy Boulevard', '328-555-2349', 'LC1'),
  ('Fanny', 'Crowne', 'Restocker', '1023 Bokanovsky Lane', '326-555-6329', 'FC1'),
  ('Helmholtz', 'Watson', 'Janitor', '944 Soma Court', '329-555-2478', 'HW1');

SHOW INDEXES FROM employees_example\G
*************************** 1. row ***************************
        Table: employees_example
   Non_unique: 0
     Key_name: PRIMARY
 Seq_in_index: 1
  Column_name: id
    Collation: A
  Cardinality: 6
     Sub_part: NULL
       Packed: NULL
         Null: 
   Index_type: BTREE
      Comment: 
Index_comment: 
      Ignored: NO
*************************** 2. row ***************************
        Table: employees_example
   Non_unique: 0
     Key_name: employee_code
 Seq_in_index: 1
  Column_name: employee_code
    Collation: A
  Cardinality: 6
     Sub_part: NULL
       Packed: NULL
         Null: 
   Index_type: BTREE
      Comment: 
Index_comment: 
      Ignored: NO
*************************** 3. row ***************************
        Table: employees_example
   Non_unique: 1
     Key_name: first_name
 Seq_in_index: 1
  Column_name: first_name
    Collation: A
  Cardinality: NULL
     Sub_part: NULL
       Packed: NULL
         Null: 
   Index_type: BTREE
      Comment: 
Index_comment: 
      Ignored: NO
*************************** 4. row ***************************
        Table: employees_example
   Non_unique: 1
     Key_name: first_name
 Seq_in_index: 2
  Column_name: last_name
    Collation: A
  Cardinality: NULL
     Sub_part: NULL
       Packed: NULL
         Null: 
   Index_type: BTREE
      Comment: 
Index_comment: 
      Ignored: NO

See Also

• Ignored Indexes

• SHOW INDEX_STATISTICS

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