单精度的浮点数会产生误差，在对精度要求比较高的应用中要使用定点数保存数据，定点数实际上是以字符串形式存放的。

mysql> create table test (c1 float(10,2),c2 double(10,2),c3 decimal(10,2));

Query OK, 0 rows affected (0.17 sec)

mysql> insert into test values(851028.52,851028.52,851028.52);

Query OK, 1 row affected (0.02 sec)

mysql> insert into test values(851028.42,851028.52,851028.52);

Query OK, 1 row affected (0.03 sec)

mysql> select * from test;

+-----------+-----------+-----------+

| c1 | c2 | c3 |

+-----------+-----------+-----------+

| 851028.50 | 851028.52 | 851028.52 |

| 851028.44 | 851028.52 | 851028.52 |

+-----------+-----------+-----------+

2 rows in set (0.00 sec)