1CREATE TABLE t2970 (a INT, b INT, c INT, d INT, KEY(a), KEY(a, b)) ENGINE=InnoDB;
2INSERT INTO t2970 VALUES (1,1,1,1), (1,2,3,4);
3EXPLAIN SELECT a, COUNT(b), MAX(b) FROM t2970 WHERE a > 0 GROUP BY a ORDER BY a;;
4id	1
5select_type	SIMPLE
6table	t2970
7type	index
8possible_keys	a,a_2
9key	a_2
10key_len	10
11ref	NULL
12rows	2
13Extra	Using where; Using index
14DROP TABLE t2970;
15