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What is the role of float and double types in mysql, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain in detail for you, people with this need can come to learn, I hope you can get something.

Float double Typ

1.float Typ

No result can be found in the default length of float column type. Precision must be specified.

For example, num float, insert into table (num) values (0.12); select * from table where num=0.12, empty set.

Num float (9 num 7), insert into table (num) values (0. 12); select * from table where num=0.12 will find this record.

Mysql > create table tt

-> (www.2cto.com

-> 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

Note: out of the field range, cannot be inserted

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)

Note: the number of decimal places is not enough, it will be filled automatically, but there is a problem that is the approximate value above.

Mysql > insert into tt (num) values (123456.867)

Query OK, 1 row affected (0.04 sec)

Mysql > select * from tt

+-+ www.2cto.com

| | 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

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

+-+ www.2cto.com

| | 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)

Note: if the number of decimal places exceeds, the approximate value will be taken automatically.

-

2.double Typ

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)

Www.2cto.com

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

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)

Www.2cto.com

FLOAT (M ~ D) or REAL (M ~ D) or DOUBLE PRECISION (M ~ D). Here, "(M _ (D))" indicates that the value shows a total of M-bit integers, where D-place is after the decimal point.

For example, a column defined as FLOAT (7p4) can be displayed as-999.9999. MySQL is rounded when saving the value, so if you insert 999.00009 into the FLOAT (7) column, the approximate result is 999.0001.

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