用INFORMATION_SCHEMA邏輯MySQL的索引

分庫分表的場景下，變更目前還不知道有哪個表變更索引失敗，是不是所有的表都變更成功了，所以可以從INFORMATION_SCHEMA通過羅列索引個數，或者查看索引行，就可以知道是不是所有的都變更成功了：

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;

也可以執行：

SELECT t.name AS `Table`,
       i.name AS `Index`,
       GROUP_CONCAT(f.name ORDER BY f.pos) AS `Columns`
FROM information_schema.innodb_sys_tables t 
JOIN information_schema.innodb_sys_indexes i USING (table_id) 
JOIN information_schema.innodb_sys_fields f USING (index_id)
WHERE t.schema = 'sakila'
GROUP BY 1,2;

參考資料：

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