mysql float double 类型
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
num float(9,7),
mysql> create table tt
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
+------------+
| 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
+------------+
| num
+------------+
| 123456.797 |
| 123456.797 |
| 123456.867 |
+------------+
3 rows in set (0.00 sec)
mysql> select
+------------+
| 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
+------------+
| num
+------------+
| 123456.797 |
| 123456.797 |
| 123456.867 |
|
+------------+
4 rows in set (0.00 sec)
mysql> select
+-------+
| 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
+------------+
| num
+------------+
| 123456.797 |
| 123456.797 |
| 123456.867 |
|
|
+------------+
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(
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
+------------+
| 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
+------------+
| 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
+------------+
| num
+------------+
| 234563.900 |
| 234563.200 |
|
+------------+
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。