How to derive value of a field from another field in MySQL?

For this, you can use the concept of user defined variable. Let us first create a table −

mysql> create table DemoTable1868
     (
     Value int
     );
Query OK, 0 rows affected (0.00 sec)

Insert some records in the table using insert command −

mysql> insert into DemoTable1868 values(10);
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1868 values(20);
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1868 values(30);
Query OK, 1 row affected (0.00 sec)
mysql> insert into DemoTable1868 values(40);
Query OK, 1 row affected (0.00 sec)

Display all records from the table using select statement −

mysql> select * from DemoTable1868;

This will produce the following output −

+-------+
| Value |
+-------+
|    10 |
|    20 |
|    30 |
|    40 |
+-------+
4 rows in set (0.00 sec)

Here is the query to derive value of a field from another field in MySQL −

mysql> select  Value,(@iterator:=Value+@iterator) as SecondColumn from DemoTable1868,( select @iterator:=0) tbl;

This will produce the following output −

+-------+--------------+
| Value | SecondColumn |
+-------+--------------+
|    10 |           10 |
|    20 |           30 |
|    30 |           60 |
|    40 |          100 |
+-------+--------------+
4 rows in set (0.00 sec)