[mysql] How to see indexes for a database or table in MySQL?

How do I see if my database has any indexes on it?

How about for a specific table?

SHOW INDEX FROM mytable FROM mydb;

SHOW INDEX FROM mydb.mytable;

See documentation.

To get all indexed columns per index in one column in the sequence order.

SELECT table_name AS `Table`,
       index_name AS `Index`,
       GROUP_CONCAT(column_name ORDER BY seq_in_index) AS `Columns`
FROM information_schema.statistics
WHERE table_schema = 'sakila'
GROUP BY 1,2;

Ref: http://blog.9minutesnooze.com/mysql-information-schema-indexes/

If you want to see all indexes across all databases all at once:

use information_schema;
SELECT * FROM statistics;

To query the index information of a table, you use the SHOW INDEXES statement as follows:

 SHOW INDEXES FROM table_name;

You can specify the database name if you are not connected to any database or you want to get the index information of a table in a different database:

SHOW INDEXES FROM table_name 
IN database_name;

The following query is similar to the one above:

SHOW INDEXES FROM database_name.table_name;

Note that INDEX and KEYS are the synonyms of the INDEXES, IN is the synonym of the FROM, therefore, you can use these synonyms in the SHOW INDEXES column instead. For example:

SHOW INDEX IN table_name 
FROM database_name;

Or

 SHOW KEYS FROM tablename
 IN databasename;

we can directly see the indexes on to the table if we know the index name with below :

select * from all_indexes where index_name= 'your index'

You could use this query to get the no of indexes as well as the index names of each table in specified database.

SELECT TABLE_NAME,
       COUNT(1) index_count,
       GROUP_CONCAT(DISTINCT(index_name) SEPARATOR ',\n ') indexes
FROM INFORMATION_SCHEMA.STATISTICS
WHERE TABLE_SCHEMA = 'mydb'
      AND INDEX_NAME != 'primary'
GROUP BY TABLE_NAME
ORDER BY COUNT(1) DESC;

To check all disabled indexes on db

SELECT INDEX_SCHEMA, COLUMN_NAME, COMMENT 
FROM information_schema.statistics
WHERE table_schema = 'mydb'
AND COMMENT = 'disabled'

You can check your indexes in MySQL workbench.under the performance reports tabs you can see all used indexes and unused indexes on the system. or you can fire the query.

select * from sys.schema_index_statistics;

This works in my case for getting table name and column name in the corresponding table for indexed fields.

SELECT TABLE_NAME , COLUMN_NAME, COMMENT 
FROM information_schema.statistics
WHERE table_schema = 'database_name';

Why not show create table myTable ?

Someone told me this but I didn't see anyone mention here, anything bad?

It's neat if you just want to take a glance at the indexes along with column infomations.

I propose this query:

SELECT DISTINCT s.*
FROM INFORMATION_SCHEMA.STATISTICS s
LEFT OUTER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS t 
    ON t.TABLE_SCHEMA = s.TABLE_SCHEMA 
       AND t.TABLE_NAME = s.TABLE_NAME
       AND s.INDEX_NAME = t.CONSTRAINT_NAME 
WHERE 0 = 0
      AND t.CONSTRAINT_NAME IS NULL
      AND s.TABLE_SCHEMA = 'YOUR_SCHEMA_SAMPLE';

You found all Index only index.

Regard.