MySQL实现了很多独特的函数，有时候使用起来是非常的方便，或许这就是开源的好处吧。这里记录一下benchmark函数，一个用于测试MySQL函数性能的函数。benchmark函数只有两个参数，第一个是执行次数，第二个是要测试的函数或者表达式。返回的结果始终是0，执行时间才是我们需要的结果：
mysql> select benchmark(1e8,current_date());
+-------------------------------+
| benchmark(1e8,current_date()) |
+-------------------------------+
| 0 |
+-------------------------------+
1 row in set (31.08 sec)
mysql> select benchmark(1e8,abs(1));
+-----------------------+
| benchmark(1e8,abs(1)) |
+-----------------------+
| 0 |
+-----------------------+
1 row in set (1.31 sec)
+-------------------------------+
| benchmark(1e8,current_date()) |
+-------------------------------+
| 0 |
+-------------------------------+
1 row in set (31.08 sec)
mysql> select benchmark(1e8,abs(1));
+-----------------------+
| benchmark(1e8,abs(1)) |
+-----------------------+
| 0 |
+-----------------------+
1 row in set (1.31 sec)
除法的效率明显不如乘法：
mysql> select benchmark(1e8,1*1);
+--------------------+
| benchmark(1e8,1*1) |
+--------------------+
| 0 |
+--------------------+
1 row in set (1.45 sec)
mysql> select benchmark(1e8,1/1);
+--------------------+
| benchmark(1e8,1/1) |
+--------------------+
| 0 |
+--------------------+
1 row in set (19.47 sec)
+--------------------+
| benchmark(1e8,1*1) |
+--------------------+
| 0 |
+--------------------+
1 row in set (1.45 sec)
mysql> select benchmark(1e8,1/1);
+--------------------+
| benchmark(1e8,1/1) |
+--------------------+
| 0 |
+--------------------+
1 row in set (19.47 sec)
