NAO sera usado, como nos exemplos abaixo:cpo_b, cpo_ccpo_bcpo_cOutros exemplos de pesquisa, aonde o indice nao sera usado:cpo_a, cpo_c (falta o cpo_b)cpo_c, cpo_a (falta o cpo_b)mysql> EXPLAIN SELECT * from tabela_a WHERE cd_reg = 1;+----+-------------+----------+-------+---------------+---------+---------+-------+------+-------+| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |+----+-------------+----------+-------+---------------+---------+---------+-------+------+-------+| 1 | SIMPLE | tabela_a | const | PRIMARY | PRIMARY | 4 | const | 1 | |+----+-------------+----------+-------+---------------+---------+---------+-------+------+-------+1 row in set (0.00 sec)mysql> EXPLAIN SELECT * from tabela_a WHERE cpo_a = 'a';+----+-------------+----------+------+---------------+--------+---------+-------+------+-------------+| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |+----+-------------+----------+------+---------------+--------+---------+-------+------+-------------+| 1 | SIMPLE | tabela_a | ref | indx01 | indx01 | 10 | const | 1 | Using where |+----+-------------+----------+------+---------------+--------+---------+-------+------+-------------+1 row in set (0.00 sec)mysql> EXPLAIN SELECT * from tabela_a WHERE cpo_a = 'd';+----+-------------+----------+------+---------------+--------+---------+-------+------+-------------+| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |+----+-------------+----------+------+---------------+--------+---------+-------+------+-------------+| 1 | SIMPLE | tabela_a | ref | indx01 | indx01 | 10 | const | 1 | Using where |+----+-------------+----------+------+---------------+--------+---------+-------+------+-------------+1 row in set (0.00 sec)mysql> EXPLAIN SELECT * from tabela_a WHERE cpo_a = 'd' and cpo_b = '2016-03-10' and cpo_c = 3;+----+-------------+----------+------+---------------+--------+---------+-------------------+------+-------------+| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |+----+-------------+----------+------+---------------+--------+---------+-------------------+------+-------------+| 1 | SIMPLE | tabela_a | ref | indx01 | indx01 | 24 | const,const,const | 1 | Using where |+----+-------------+----------+------+---------------+--------+---------+-------------------+------+-------------+1 row in set, 2 warnings (0.01 sec)mysql> EXPLAIN SELECT * from tabela_a WHERE cpo_a = 'd' and cpo_b = '2016-03-10';+----+-------------+----------+------+---------------+--------+---------+-------------+------+-------------+| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |+----+-------------+----------+------+---------------+--------+---------+-------------+------+-------------+| 1 | SIMPLE | tabela_a | ref | indx01 | indx01 | 15 | const,const | 1 | Using where |+----+-------------+----------+------+---------------+--------+---------+-------------+------+-------------+1 row in set (0.00 sec)mysql> EXPLAIN SELECT * from tabela_a WHERE cpo_a = 'd';+----+-------------+----------+------+---------------+--------+---------+-------+------+-------------+| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |+----+-------------+----------+------+---------------+--------+---------+-------+------+-------------+| 1 | SIMPLE | tabela_a | ref | indx01 | indx01 | 10 | const | 1 | Using where |+----+-------------+----------+------+---------------+--------+---------+-------+------+-------------+1 row in set (0.00 sec)mysql> EXPLAIN SELECT * from tabela_a WHERE cpo_a = 'd' and cpo_c = '2016-03-10' and cpo_b = 3;+----+-------------+----------+------+---------------+--------+---------+-------------------+------+-------------+| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |+----+-------------+----------+------+---------------+--------+---------+-------------------+------+-------------+| 1 | SIMPLE | tabela_a | ref | indx01 | indx01 | 24 | const,const,const | 1 | Using where |+----+-------------+----------+------+---------------+--------+---------+-------------------+------+-------------+1 row in set (0.00 sec)mysql> EXPLAIN SELECT * from tabela_a WHERE cpo_c = '2016-03-10' and cpo_b = 3;+----+-------------+----------+------+---------------+------+---------+------+------+-------------+| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |+----+-------------+----------+------+---------------+------+---------+------+------+-------------+| 1 | SIMPLE | tabela_a | ALL | NULL | NULL | NULL | NULL | 2 | Using where |+----+-------------+----------+------+---------------+------+---------+------+------+-------------+1 row in set (0.00 sec)mysql> EXPLAIN SELECT * from tabela_a WHERE cpo_b = 3;+----+-------------+----------+------+---------------+------+---------+------+------+-------------+| id | select_type | table | type | possible_keys | key | key_len |