MySQL float double type

1.float type
Float column Type default length cannot find results, you must specify precision,
For example , num float, INSERT into table (num) values (0.12); Select * from table where num=0.12, empty set.
Num Float (9,7), insert into table (num) values (0.12); Select * FROM table where num=0.12 will find this record.

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 to column ' num ' at row 1
Note: Out of field range, unable to insert

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 digits is not enough, auto-fill, but there is a problem 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;
+------------+
| 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)
Note: The number of decimal digits is super, the approximate value is automatically taken.

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2.double type

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 * 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 to 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) or real (m,d) or double PRECISION (m,d). Here, "(M,d)" indicates that the value displays a total of M-bit integers, where the D-bit is behind the decimal point.
For example, a column defined as float (7,4) can be displayed as-999.9999. MySQL is rounded when the value is saved, so if you insert 999.00009 in float (7,4) aligns, the approximate result is 999.0001.