如何查看 MySQL 中的数据库或表的索引？

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

How about for a specific table?

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.

SHOW INDEX FROM mytable FROM mydb;

SHOW INDEX FROM mydb.mytable;

See documentation.

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

use information_schema;
SELECT * FROM statistics;

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.

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;

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;

To check all disabled indexes on db

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

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';