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，
比如 num<wbr> float,<wbr> insert into<wbr> table (num) values (0.12); select<wbr> * from table where num=0.12的话，empty set。<br> num float(9,7),<wbr> insert into<wbr> table (num) values (0.12); select<wbr> * from table where num=0.12的话会查到这条记录。</wbr></wbr></wbr></wbr></wbr></wbr></wbr>

mysql> create table tt
<wbr><wbr><wbr> -&gt; (<br><wbr><wbr><wbr> -&gt; num<wbr> float(9,3)<br><wbr><wbr><wbr> -&gt; );<br> Query OK, 0 rows affected (0.03 sec)</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

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<wbr> * from<wbr> tt;<br> +------------+<br> | num<wbr><wbr><wbr><wbr><wbr><wbr><wbr> |<br> +------------+<br> | 123456.797 |<br> +------------+<br> 1 row in set (0.00 sec)<br> 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。</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

mysql> insert into tt(num)values(123456.867);
Query OK, 1 row affected (0.04 sec)

mysql> select * from<wbr><wbr> tt;<br> +------------+<br> | num<wbr><wbr><wbr><wbr><wbr><wbr><wbr> |<br> +------------+<br> | 123456.797 |<br> | 123456.797 |<br> | 123456.867 |<br> +------------+<br> 3 rows in set (0.00 sec)</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

mysql> select<wbr> * from tt where<wbr> num=123456.867;<br> +------------+<br> | num<wbr><wbr><wbr><wbr><wbr><wbr><wbr> |<br> +------------+<br> | 123456.867 |<br> +------------+<br> 1 row in set (0.00 sec)</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

mysql> insert into tt(num)values(2.8);
Query OK, 1 row affected (0.04 sec)

mysql> select * from<wbr><wbr> tt;<br> +------------+<br> | num<wbr><wbr><wbr><wbr><wbr><wbr><wbr> |<br> +------------+<br> | 123456.797 |<br> | 123456.797 |<br> | 123456.867 |<br> |<wbr><wbr><wbr><wbr><wbr> 2.800 |<br> +------------+<br> 4 rows in set (0.00 sec)</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

mysql> select<wbr> * from tt where<wbr> num=2.8;<br> +-------+<br> | num<wbr><wbr> |<br> +-------+<br> | 2.800 |<br> +-------+<br> 1 row in set (0.00 sec)</wbr></wbr></wbr></wbr>

mysql> insert into tt(num)values(2.888888);
Query OK, 1 row affected (0.00 sec)

mysql> select<wbr> * from<wbr> tt;<br> +------------+<br> | num<wbr><wbr><wbr><wbr><wbr><wbr><wbr> |<br> +------------+<br> | 123456.797 |<br> | 123456.797 |<br> | 123456.867 |<br> |<wbr><wbr><wbr><wbr><wbr> 2.800 |<br> |<wbr><wbr><wbr><wbr><wbr> 2.889 |<br> +------------+<br> 5 rows in set (0.00 sec)<br> 注：小数位数超了，自动取近似值。</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

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2.double类型

mysql> create table tt(
<wbr><wbr><wbr> -&gt; num<wbr> double(9,3)<br><wbr><wbr><wbr> -&gt; );<br> Query OK, 0 rows affected (0.02 sec)</wbr></wbr></wbr></wbr></wbr></wbr></wbr>

mysql> insert into tt(num) values(234563.9);
Query OK, 1 row affected (0.00 sec)

mysql> select * from<wbr> tt;<br> +------------+<br> | num<wbr><wbr><wbr><wbr><wbr><wbr><wbr> |<br> +------------+<br> | 234563.900 |<br> +------------+<br> 1 row in set (0.00 sec)</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

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<wbr> * from<wbr> tt;<br> +------------+<br> | num<wbr><wbr><wbr><wbr><wbr><wbr><wbr> |<br> +------------+<br> | 234563.900 |<br> | 234563.200 |<br> +------------+<br> 2 rows in set (0.00 sec)</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

mysql> insert into tt(num) values(2.8);
Query OK, 1 row affected (0.00 sec)

mysql> select<wbr> * from tt;<br> +------------+<br> | num<wbr><wbr><wbr><wbr><wbr><wbr><wbr> |<br> +------------+<br> | 234563.900 |<br> | 234563.200 |<br> |<wbr><wbr><wbr><wbr><wbr> 2.800 |<br> +------------+<br> 3 rows in set (0.00 sec)<br></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr></wbr>

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。