We help IT Professionals succeed at work.
Get Started

Difference between an Inner-Join and an Equi-Join in SQL Server 2008

Last Modified: 2018-04-01
I have 2 tables called 'table123' and 'table246'.

'table123' columns: 'ID', 'Dept_ID', 'First_Name', 'Surname', 'Salary', 'Address'.

'table246' columns: 'Dept_ID', 'Dept_Name'.

I want to find the list of employees with the lowest salary per department. Two of the ways I can do it is an Equi-Join or an Inner-Join. I've been told they can both be used to provide the desired result.

The queries I used:


SELECT First_Name, b.Dept_Name, alt.Min_Salary AS Min_Salary
FROM table123 a, table246 b,
(SELECT Dept_ID, MIN(Salary)Min_Salary
FROM table123
GROUP BY Dept_ID)alt
WHERE a.Dept_ID = b.Dept_ID
AND a.salary = alt.Min_Salary
AND a.Dept_ID = alt.Dept_ID;

Open in new window

Inner Join:

SELECT MIN(Salary)Min_Salary, Dept_Name
FROM table123 a, table246 b
INNER JOIN (SELECT First_Name, MIN(Salary)
FROM table123
GROUP BY Dept_ID)alt
ON b.Dept_ID = alt.Dept_ID;

Open in new window

The Equi-Join statement gives me the desired table, containing the columns 'First_Name', 'Dept_Name' & 'Min_Salary', with all relevant data.

However, the Inner-Join statement doesn't run because the First_Name column needs to be included in the aggregate function or GROUP BY clause. This really confuses me, as I don't know how to go about fixing it. How can I adjust the Inner-Join query, so as to give the same result as the Equi-Join query?
Watch Question
EE Topic Advisor
Most Valuable Expert 2014
Awarded 2013
This problem has been solved!
Unlock 2 Answers and 5 Comments.
See Answers
Why Experts Exchange?

Experts Exchange always has the answer, or at the least points me in the correct direction! It is like having another employee that is extremely experienced.

Jim Murphy
Programmer at Smart IT Solutions

When asked, what has been your best career decision?

Deciding to stick with EE.

Mohamed Asif
Technical Department Head

Being involved with EE helped me to grow personally and professionally.

Carl Webster
CTP, Sr Infrastructure Consultant
Ask ANY Question

Connect with Certified Experts to gain insight and support on specific technology challenges including:

  • Troubleshooting
  • Research
  • Professional Opinions
Did You Know?

We've partnered with two important charities to provide clean water and computer science education to those who need it most. READ MORE