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- /*
- SQL script to grab the worst performing indexes
- in the whole server
- */
- SELECT
- t.TABLE_SCHEMA AS `db`
- , t.TABLE_NAME AS `table`
- , s.INDEX_NAME AS `inde name`
- , s.COLUMN_NAME AS `field name`
- , s.SEQ_IN_INDEX `seq in index`
- , s2.max_columns AS `# cols`
- , s.CARDINALITY AS `card`
- , t.TABLE_ROWS AS `est rows`
- , ROUND(((s.CARDINALITY / IFNULL(t.TABLE_ROWS, 0.01)) * 100), 2) AS `sel %`
- FROM INFORMATION_SCHEMA.STATISTICS s
- INNER JOIN INFORMATION_SCHEMA.TABLES t
- ON s.TABLE_SCHEMA = t.TABLE_SCHEMA
- AND s.TABLE_NAME = t.TABLE_NAME
- INNER JOIN (
- SELECT
- TABLE_SCHEMA
- , TABLE_NAME
- , INDEX_NAME
- , MAX(SEQ_IN_INDEX) AS max_columns
- FROM INFORMATION_SCHEMA.STATISTICS
- WHERE TABLE_SCHEMA != 'mysql'
- GROUP BY TABLE_SCHEMA, TABLE_NAME, INDEX_NAME
- ) AS s2
- ON s.TABLE_SCHEMA = s2.TABLE_SCHEMA
- AND s.TABLE_NAME = s2.TABLE_NAME
- AND s.INDEX_NAME = s2.INDEX_NAME
- WHERE t.TABLE_SCHEMA != 'mysql' /* Filter out the mysql system DB */
- AND t.TABLE_ROWS > 10 /* Only tables with some rows */
- AND s.CARDINALITY IS NOT NULL /* Need at least one non-NULL value in the field */
- AND (s.CARDINALITY / IFNULL(t.TABLE_ROWS, 0.01)) < 1.00 /* Selectivity < 1.0 b/c unique indexes are perfect anyway */
- ORDER BY `sel %`, s.TABLE_SCHEMA, s.TABLE_NAME /* Switch to `sel %` DESC for best non-unique indexes */
- LIMIT 10;
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