Question

I have a table FOLDERS,everytime a folder is added through a php page it gets inserted into FOLDERS.
each folder has these fields: id,userid,foldername

I simplified the table to make my question easier to grasp.

ID UID FOLDERNAME

1 – 1 – Books

2 – 1 – Receipts

3 – NULL – Books

4 – NULL – Receipts

5 – NULL – Home

6 – 2 – Receipts

I would like to know how to get the fifth row as a result.
The condition would be: The fact that row 5 doesnt have any UID (its empty) and is doesn’t exist with a uid. When I use:

$sql="SELECT * FROM folders WHERE  userid=''";

this returns ALL the rows with an empty userid. I only want 5 as a result because UID=1 already has his folder Receipts and Books set.
any suggestions would help I ve been struggling with this for a couple of hours now. Thank you

Answer 1

Combine a condition userid IS NULL for null userid rows with a NOT IN() subquery which returns all the distinct folder names which do have a userid in other rows.

SELECT *
FROM hpoptions
WHERE 
  userid IS NULL 
  AND foldername NOT IN (
    SELECT DISTINCT foldername FROM hpoptions WHERE userid IS NOT NULL
  )