How to add n number of columns to an existing table,the new columns should have the aggregate of an existing column

Question

I have a table like:

ID NAME SALARY
1  JOSE 100
2  KEVI 100
3  JAMS 200
4  SANJ 400

I need to get the output like:

ID NAME SALARY SALARY-1 SALARY-2 SALARY-3 SALARY-4 
1  JOSE  100   99       98       97       96
2  KEVI  100   99       98       97       96
3  JAMS  200   199      198      197      196
4  SANJ  400   399      398      397      396

How can I get the desired table?

Answer 1

If you just want output, then use a query:

select id, name, salary, salary-1, salary-2, salary-3, salary-4
from table t;

If you actually want to add these columns to the table, you can use alter table add column and then update the values.

Answer 2

Use this stored procedure to get your result. This is working for me. Please change the table and column name as per your db.

DELIMITER $$
DROP PROCEDURE IF EXISTS my_proc$$

CREATE PROCEDURE my_proc(n INT)
proc : BEGIN

SET @q = CONCAT('SELECT ID, NAME, SALARY');
SET @num = 1;

select_loop : LOOP

    SET @q = CONCAT(@q, ', SALARY - ',@num);

    IF n = 0 THEN
        LEAVE select_loop;
    END IF;

    SET n = n - 1;
    SET @num = @num + 1;

END LOOP;

SET @q = CONCAT(@q, ' FROM sal');

PREPARE stmt FROM @q;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

END$$

DELIMITER ;

Call the stored procedure with the number of salary columns you want in output

mysql> CALL my_proc(4);
+----+------+--------+------------+------------+------------+------------+------------+
| ID | NAME | SALARY | SALARY - 1 | SALARY - 2 | SALARY - 3 | SALARY - 4 | SALARY - 5 |
+----+------+--------+------------+------------+------------+------------+------------+
|  1 | jose |    100 |         99 |         98 |         97 |         96 |         95 |
|  2 | kevi |    100 |         99 |         98 |         97 |         96 |         95 |
|  3 | jams |    200 |        199 |        198 |        197 |        196 |        195 |
|  4 | sanj |    400 |        399 |        398 |        397 |        396 |        395 |
+----+------+--------+------------+------------+------------+------------+------------+
4 rows in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)