Convert string (varchar) to double in MySQL

Let us first create a table:

mysql> create table DemoTable731 (Value varchar(100));
Query OK, 0 rows affected (0.50 sec)

Insert some records in the table using insert command -

mysql> insert into DemoTable731 values('4.50');
Query OK, 1 row affected (0.15 sec)
mysql> insert into DemoTable731 values('7.83');
Query OK, 1 row affected (0.18 sec)
mysql> insert into DemoTable731 values('8.91');
Query OK, 1 row affected (0.25 sec)
mysql> insert into DemoTable731 values('560.34');
Query OK, 1 row affected (0.21 sec)

Display all records from the table using select statement -

mysql> select *from DemoTable731;

This will produce the following output -

+--------+
| Value  |
+--------+
| 4.50   |
| 7.83   |
| 8.91   |
| 560.34 |
+--------+
4 rows in set (0.00 sec)

Here is the query to convert string to double -

mysql> select Value+0.0 AS demo from DemoTable731;

This will produce the following output -

+-----------+
| demo      |
+-----------+
| 4.5       |
| 7.83      |
| 8.91      |
| 560.34    |
+-----------+
4 rows in set (0.28 sec)