Most of SQL queries have no math operation on where clause.
What is wrong having them on 'where clause'? Is there any performance issue?
Eg:
SELECT * FROM Employee WHERE Salary*3 = 5000
If a where clause can use an index, it is often (but not always) faster. Using a math operation on a field will prevent the index from being used.
For example, if you had a table with a million rows and a date column that was indexed, query 1 here would by far outperform query 2 (they both retrieve all rows where the date is in the last 7 days):
query 1:
select date from table where date > dateadd(d, -7, getdate())
query 2:
select date from table where dateadd(d, 7, date) > getdate()
In your example, the query would be far better as:
select * from employee where salary = (5000 / 3)