'NOT IN' and 'IN' clause return the same?

Question

1.67/5 (2 votes)

See more:

Hi Everyone, I'm very new to SQL and am having difficulty understanding why my IN and NOT IN clause is returning the same results when I write my query.

I have three tables: TableA,TableB, and TableC. A fourth table has a table of our plants. I am trying to return all the data from TableC that isn't linked to a valid Plants.ID

SQL

SELECT TableC.* FROM TablePlants
  JOIN TableA ON TablePlants.ID = TableA.Plant_ID
  JOIN TableB ON TableA.ID = TableB.TableA_ID
  JOIN TableC ON TableB.ID = TableC.TableB_ID
   WHERE EXISTS( select * FROM TableA 
    WHERE TableA.Plant_ID NOT IN (select TablePlants.ID FROM TablePlants))

Whether I have 'NOT IN' or just 'IN' it returns only those entries which are IN TablePlants.

What am I missing?

Thanks a ton for any help!

Posted 22-Oct-13 10:44am

MrGlass3

Add a Solution

1 solution

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)

phil.o · Accepted Answer · 2013-10-22T11:57:00

SQL

SELECT
  TableC.ID
 --,TableC.SomeColumn1
 --,TableC.SomeColumn2
FROM TableC LEFT JOIN TableB ON TableB.ID = TableC.TableB_ID
 LEFT JOIN TableA ON TableA.ID = TableB.TableA_ID
WHERE TableA.Plant_ID NOT IN (SELECT ID FROM TablePlants)
 --AND TableA.Plant_ID IS NOT NULL --eventually

I encourage you to ban SELECT * from your vocabulary, as it is a quite bad practice :)

If you put some constraint enforcements on your foreign keys, this situation would not happen anymore.

For example

SQL

ALTER TABLE TableA
 WITH CHECK ADD CONSTRAINT FK_TableA_TablePlants
 FOREIGN KEY (Plant_ID)
 REFERENCES TablePlants (ID)
 ON UPDATE CASCADE
 ON DELETE CASCADE --SET DEFAULT could be an option here
GO