Question

What is wrong with the following to find the total salary

select sum(sal) from (
(select sal from emp where comm is null)
union
(select sal from emp where comm is not null))

Answer 1

The provided query is incorrect for calculating total salary because using UNION to combine rows where comm is null with rows where comm is not null is redundant. The total salary can be calculated with a single SUM(sal) function applied to the entire emp table.

Step-by-step explanation:

The query in the question is attempting to calculate the total salary by using a UNION to combine the results of two separate queries. However, this approach is not necessary and is incorrect because the UNION is being used in an inefficient and redundant manner. To calculate the total salary from the emp table, you can simply use the SUM function on the salary column without separating the data by whether the comm column is null or not. Here's a corrected version of the query:

SELECT SUM(sal) FROM emp;

This will provide you with the total salary of all employees regardless of their commission (comm) status.