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

问题

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

How about for a specific table?

回答1:

To see the index for a specific table use SHOW INDEX:

SHOW INDEX FROM yourtable;

To see indexes for all tables within a specific schema you can use the STATISTICS table from INFORMATION_SCHEMA:

SELECT DISTINCT
    TABLE_NAME,
    INDEX_NAME
FROM INFORMATION_SCHEMA.STATISTICS
WHERE TABLE_SCHEMA = 'your_schema';

Removing the where clause will show you all indexes in all schemas.

回答2:

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

use information_schema;
SELECT * FROM statistics;

回答3:

SHOW INDEX FROM mytable FROM mydb;

SHOW INDEX FROM mydb.mytable;

See documentation.

回答4:

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;

回答5:

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.

回答6:

To check all disabled indexes on db

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

回答7:

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';

回答8:

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;

回答9:

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/

来源：https://stackoverflow.com/questions/5213339/how-to-see-indexes-for-a-database-or-table-in-mysql

标签

mysql

indexing

database-schema