mysql float double 类型_MySQL
| 1.float类型 float列类型默认长度查不到结果，必须指定精度，比如 numfloat,insert intotable (num) values (0.12); select* from table where num=0.12的话，empty set。 num float(9,7),insert intotable (num) values (0.12); select* from table where num=0.12的话会查到这条记录。 mysql> create table tt -> ( -> numfloat(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* fromtt; +------------+ | num| +------------+ | 123456.797 | +------------+ 1 row in set (0.00 sec) 注：小数位数不够，自动补齐，但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 * fromtt; +------------+ | num| +------------+ | 123456.797 | | 123456.797 | | 123456.867 | +------------+ 3 rows in set (0.00 sec) mysql> select* from tt wherenum=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 * fromtt; +------------+ | num| +------------+ | 123456.797 | | 123456.797 | | 123456.867 | |2.800 | +------------+ 4 rows in set (0.00 sec) mysql> select* from tt wherenum=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* fromtt; +------------+ | 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，自动取近似值。 -------------------------------------------------------------------------------------- 2.double类型 mysql> create table tt( -> numdouble(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 * fromtt; +------------+ | 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* fromtt; +------------+ | 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，其中D位位于小数点后面。例如，定义为FLOAT(7,4)的一个列可以显示为-999.9999。MySQL保存值时进行四舍五入，因此如果在FLOAT(7,4)列内插入999.00009，近似结果是999.0001。 |