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)