1.float类型float列类型默认长度查不到结果。必须指定精度。 比方 num float, insert into table (num) values (0.12); select * from table where num=0.12的话。empty set。 num float(9,7), insert into table (num) values (0.12); select * from table where num=0.12的话会查到这条记录。
mysql> create table tt-> (-> num float(9,3)-> ); Query OK, 0 rows affected (0.03 sec)
mysql> insert into tt(num)values(1234567.8); ERROR 1264 (22003): Out of range value for column 'num' at row 1 注：超出字段范围，无法插入
mysql> insert into tt(num)values(123456.8); Query OK, 1 row affected (0.00 sec)
mysql> select * from tt; +------------+ | num | +------------+ | 123456.797 | +------------+ 1 row in set (0.00 sec) 注：小数位数不够，自己主动补齐，可是存在一个问题就是如上的近似值。
mysql> insert into tt(num)values(123456.867); Query OK, 1 row affected (0.04 sec)
mysql> select * from tt; +------------+ | num | +------------+ | 123456.797 | | 123456.797 | | 123456.867 | +------------+ 3 rows in set (0.00 sec)
mysql> select * from tt where num=123456.867; +------------+ | num | +------------+ | 123456.867 | +------------+ 1 row in set (0.00 sec)
mysql> insert into tt(num)values(2.8); Query OK, 1 row affected (0.04 sec)
mysql> select * from tt; +------------+ | num | +------------+ | 123456.797 | | 123456.797 | | 123456.867 | | 2.800 | +------------+ 4 rows in set (0.00 sec)
mysql> select * from tt where num=2.8; +-------+ | num | +-------+ | 2.800 | +-------+ 1 row in set (0.00 sec)
mysql> insert into tt(num)values(2.888888); Query OK, 1 row affected (0.00 sec)
mysql> select * from tt; +------------+ | num | +------------+ | 123456.797 | | 123456.797 | | 123456.867 | | 2.800 | | 2.889 | +------------+ 5 rows in set (0.00 sec) 注：小数位数超了，自己主动取近似值。
--------------------------------------------------------------------------------------
2.double类型
mysql> create table tt(-> num double(9,3)-> ); Query OK, 0 rows affected (0.02 sec)
mysql> insert into tt(num) values(234563.9); Query OK, 1 row affected (0.00 sec)
mysql> select * from tt; +------------+ | num | +------------+ | 234563.900 | +------------+ 1 row in set (0.00 sec)
mysql> insert into tt(num) values(2345623.2); ERROR 1264 (22003): Out of range value for column 'num' at row 1 mysql> insert into tt(num) values(234563.2); Query OK, 1 row affected (0.00 sec)
mysql> select * from tt; +------------+ | num | +------------+ | 234563.900 | | 234563.200 | +------------+ 2 rows in set (0.00 sec)
mysql> insert into tt(num) values(2.8); Query OK, 1 row affected (0.00 sec)
mysql> select * from tt; +------------+ | num | +------------+ | 234563.900 | | 234563.200 | | 2.800 | +------------+ 3 rows in set (0.00 sec)
FLOAT(M,D)或REAL(M,D)或DOUBLE PRECISION(M,D)。这里，“(M,D)”表示该值一共显示M位整数。当中D位位于小数点后面。 比如，定义为FLOAT(7,4)的一个列能够显示为-999.9999。
MySQL保存值时进行四舍五入，因此假设在FLOAT(7,4)列内插入999.00009，近似结果是999.0001。
转载于:https://www.cnblogs.com/bhlsheji/p/5077565.html
相关资源：数据结构—成绩单生成器