Question

If I run

Select distinct CompanyID from Device 

I get 6 rows. If I run

Select CompanyID from Company

I get 8441 rows. If I run the following:

If I run

Select CompanyID
from Company where CompanyID NOT IN 
( 
   Select distinct CompanyID from Device
)

I should get the 8435 companies that aren’t in the original select statement, correct?

However, when I run this I get 0 rows. What is the issue here? One of the 6 results from above is null but that shouldn’t matter.

Thanks!

edit: With Marc-s’s help I was able to get the following statement to be what I needed, I still feel like there was an extra step in this query, anyone care to add to this?

DELETE from Company where CompanyID NOT IN
(
Select C.CompanyID 
from Company C where C.CompanyID IN 
( 
  Select distinct CompanyID from Device
)
OR CompanyID IN
(
  Select distinct CustomerID from Device
)
OR CompanyID IN
(
  Select distinct CompanyID from AssignedCompanies
 )
 )

Answer 1

Assuming there are CompanyIDs in Company that are not in Device, the problem is the NULL value in the 6 from Device. Your NOT IN statement evaluates to UNKNOWN even if the CompanyID is not one of the 6. See this Q/A for more details: NOT IN clause and NULL values

Edit: To avoid this try altering your subquery to:

SELECT DISTINCT CompanyID FROM  Device WHERE CompanyID IS NOT NULL