Question

I have a MySQL database with a relationship table which can be simplified to:

CREATE TABLE `Paths` (
  `origin` char(32) NOT NULL,
  `destination` char(32) NOT NULL,
  `id` int(11) NOT NULL AUTO_INCREMENT,
  PRIMARY KEY  (`id`),
)

This is a many-to-many relationship.
I want to delete all paths where all paths from that origin only lead to a certain place, e.g. Neverland.

This SQL should work:

DELETE FROM Paths WHERE origin IN (SELECT DISTINCT origin FROM Paths WHERE destination = 'Neverland') AND origin NOT IN (SELECT DISTINCT origin FROM Paths WHERE destination <> 'Neverland');

But, is there a better, more efficient way?

Thanks!

Answer 1

Try:

  Delete Paths
  From Paths p
  Where Not Exists  
      (Select * From paths 
       Where Origin = p.origin
       And Destination <> 'Neverland')