-- How useful is an index (in percentage likeliness of hits):

SELECT
t.TABLE_SCHEMA
, t.TABLE_NAME
, s.INDEX_NAME
, s.COLUMN_NAME
, s.SEQ_IN_INDEX
, (
SELECT MAX(SEQ_IN_INDEX)
FROM INFORMATION_SCHEMA.STATISTICS s2
WHERE s.TABLE_SCHEMA = s2.TABLE_SCHEMA
AND s.TABLE_NAME = s2.TABLE_NAME
AND s.INDEX_NAME = s2.INDEX_NAME
) AS "COLS_IN_INDEX"
, s.CARDINALITY AS "CARD"
, t.TABLE_ROWS AS "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
WHERE t.TABLE_SCHEMA != 'mysql'
AND t.TABLE_ROWS > 10
AND s.CARDINALITY IS NOT NULL
AND (s.CARDINALITY / IFNULL(t.TABLE_ROWS, 0.01)) < 1.00
ORDER BY t.TABLE_SCHEMA, t.TABLE_NAME, s.INDEX_NAME, "SEL %";