Raising salary by 15% using SQL only? - sql

Question

I am trying to modify the SCOTT schema by raising employees salaries by 15%. If the resulting salary exceeds his or her highest possible salary, HISAL, in SALGRADE we just use HISAL, my code is:
select
coalesce((
select sal*1.15
from emp , salgrade
where
sal*1.15<=hisal
) ,
(select hisal from emp ,salgrade where sal*1.15>hisal )) raised_sal
from emp ;
The inner select returns multiple rows
Does anyone have suggestions or different code?

Answer 1

If we break-down what you're trying to do:
coalesce gives the first value, unless that is null then the second etc. You haven't specified any join condition, so you're doing a cartesian join between emp and salgrade. This will return the number of rows in emp multiplied by the number of rows in salgrade; subject to your join condition.
The second part of your query does exactly the same in the opposite direction.
Assuming a table_structure of:
create table emp (
emp_id number
, salary number -- current salary
, salgrade_id number -- current salary grade
, dept_id -- current department
);
create table salgrade (
, salgrade_id number
, hisal number -- max salary for that grade
);
You want to be doing something like this:
select least( e.salary * 1.15, s.hisal )
from emp e
join salgrade s
on e.salgrade_id = s.salgrade_id
The least function is similar to min; in that it will take the minimum value. However, it works over multiple columns on the same row, rather than multiple rows over the same column.
By taking the least of hisal and salary * 1.15 we ensure that if the salary increase is higher than hisal then hisal is taken instead.
In this case join means that for every emp_id we're taking the hisal for the appropriate salary grade. I would highly recommend reading up on SQL joins - this link was 7th on Google, which was a bit of a surprise ( Jeff seems to be everywhere ), but it's quite good and has many more links.
To change the query to enable you to do it for all employees earning over 100,000 ( the rich get richer ) it would look something like this:
select least( e.salary * 1.15, s.hisal )
from emp e
join salgrade s
on e.salgrade_id = s.salgrade_id
where e.salary > 100000
Or to complicate matters if you wanted to do it for only IT peoples ( why not ), you could extend it to something like this:
select least( e.salary * 1.15, s.hisal )
from emp e
join salgrade s
on e.salgrade_id = s.salgrade_id
join dept d
on e.dept_id = d.dept_id
where d.dept = 'IT'
These joins by being inner joins as opposed to outer joins ( normally left outer joins - see the link ) imply that every employee has a grade and a department.

Answer 2

You should join emp with salgrade through a non equijoin:
select sal*1.15
from
emp
inner join
salgrade sg
on emp.sal BETWEEN sg.losal AND sg.hisal <-- here!
where
sal*1.15<=hisal
More info: Introduction to Basic SQL, Part 3 - Complex Joins and Sub-queries:
"we joined using the BETWEEN operator. The paybands in the SALGRADE
table use a range of salary to designate a grade."
EDIT
To calculate the employee grade you should look for employee salary and look into salgrade for a salary range that contains employee salary.
This is the salgrade data:
...
INSERT INTO SALGRADE VALUES (2,1201,1400);
INSERT INTO SALGRADE VALUES (3,1401,2000);
...
If employee salary is 1495 that means that his grade is 2.
If you increase 1395 in 15% then this is out of range of your salrange and, as you explain, you should set salary at 1400 that is the hisal for range 2.
Your query:
select
coalesce((
select sal*1.15
from emp e2
inner join
salgrade sg
on e2.sal BETWEEN sg.losal AND sg.hisal
where
e2.EMPNO = e1.EMPNO and
sal*1.15<=hisal
) ,
(select hisal from emp e2 inner join salgrade sg
on e2.sal BETWEEN sg.losal AND sg.hisal
where e2.EMPNO = e1.EMPNO
)) raised_sal
from emp e1 ;
Without subqueries:
select
case
when sal*1.15 < hisal then sal*1.15
when sal*1.15 >= hisal then hisal
end
raised_sal
from
emp e1
inner join
salgrade sg
on e1.sal BETWEEN sg.losal AND sg.hisal
Disclaimer, not tested.

Answer 3

I think you missed only join condition ...
in both the query you can give join condition, if any (like emp.employee_name = salgrade.employee_name)
and have to give inner query condition also...
like
select
coalesce((
select sal*1.15
from emp e2, salgrade
where
sal*1.15<=hisal
and e2.employee_name = e1.employee_name
) ,
(select hisal from emp e3,salgrade where sal*1.15>hisal
and e3.employee_name = e1.emplyee_name
)) raised_sal
from emp e1;