select(*)这个操作 在存储引擎MyISAM会比存储引擎Innodb的查询速度快
#MyISAM
mysql> select count(*) from sbtest1;
+----------+
| count(*) |
+----------+
| 800000 |
+----------+
1 row in set (0.47 sec)
#切换存储引擎为innodb
mysql> alter table sbtest1 ENGINE=innodb ;
Query OK, 800000 rows affected (45.84 sec)
Records: 800000 Duplicates: 0 Warnings: 0
mysql> select count(*) from sbtest1;
+----------+
| count(*) |
+----------+
| 800000 |
+----------+
1 row in set (2.43 sec)
哈哈，就是这么快,还有下文
mysql> explain select count(*) from sbtest1;
+----+-------------+---------+------------+-------+---------------+------+---------+------+--------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+-------+---------------+------+---------+------+--------+----------+-------------+
| 1 | SIMPLE | sbtest1 | NULL | index | NULL | k_1 | 4 | NULL | 789120 | 100.00 | Using index |
+----+-------------+---------+------------+-------+---------------+------+---------+------+--------+----------+-------------+
1 row in set, 1 warning (0.39 sec)
mysql> alter table sbtest1 ENGINE=myisam;
Query OK, 800000 rows affected (20.63 sec)
Records: 800000 Duplicates: 0 Warnings: 0
mysql> explain select count(*) from sbtest1;
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+------------------------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+------------------------------+
| 1 | SIMPLE | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | Select tables optimized away |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+------------------------------+
1 row in set, 1 warning (0.06 sec)
