Difference between isnull and operator(! =)

Question

1.00/5 (4 votes)

See more:

Hi,

Can anyone please tell me the difference between isnull function is != operator.

What I have tried:

For Example
I want to find employees who do not have manager or whose manager is NULL.
What should i use ISNULL function or != operator and which approach is good? and why?

EmpID	EmpName	ManagerID
1	Gayatri	1
2	Radhika	[NULL]
3	Chetan	[NULL]
4	Ankur	5
5	Chhuts	11

Posted 25-May-17 14:24pm

Member 12673779

Updated 25-May-17 21:48pm

PIEBALDconsult

v2

Add a Solution

Comments

PIEBALDconsult 25-May-17 20:31pm

Yes.

Robert Welliever 25-May-17 20:56pm

Just curious, if the employees who don't have a manager are null, how else are you designating employees who do not have a manager? It seems you would only need to check for null. If you are just checking for null you might go with what is most common, i.e.:

SELECT * FROM Employees WHERE ManagerID IS NULL

Robert Welliever 26-May-17 17:05pm

I see the solution was selected, but the solution did not address your question accurately in that checking IS NULL and using the ISNULL function are two different things. You might want to understand that nuance. Also on a best practices level, don't use !=, instead use <>. Many large organizations (like Microsoft) deprecated the use of != (although still supported). Although I'm not entirely sure why it was deprecated (maybe SQL-92 Standard?) I wouldn't create habits against best practices without cause.

2 solutions

Solution 2

You should use IS NOT NULL instead of using !=,

!= will not going to provide a result

If you want to use != then You should use

SELECT * FROM MyTable WHERE ISNULL(Manager,0) != 0

Let me know if you want further more explanation.

Posted 25-May-17 21:48pm

Nirav Prabtani

v2

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

OriginalGriff · Accepted Answer · 2017-05-25T19:53:00

Try it.
You will get different results...

SQL

SELECT * FROM MyTable WHERE Manager != NULL

Will give you no rows.

SQL

SELECT * FROM MyTable WHERE Manager IS NOT NULL

Will give you rows where there is a manager.
Why? Because according to W3Schools[^] "It is not possible to test for NULL values with comparison operators, such as =, <, or <>."
NULLs propagate through expressions - anything involving a NULL value results in NULL. So when you use a condition involving an equality operator and one of the sides is NULL, the result is not TRUE or FALSE, it's NULL.
In fact, both of these will produce the same results:

SQL

SELECT * FROM MyTable WHERE Manager != NULL

SQL

SELECT * FROM MyTable WHERE Manager = NULL

Both give you no rows!