SQL DELETE with JOIN another table for WHERE condition

Question

I have to delete rows from guide_category that have no relation with guide table (dead relations).

Here is what I want to do, but it of cou

Answer 1

How about:

DELETE guide_category  
  WHERE id_guide_category IN ( 

        SELECT id_guide_category 
          FROM guide_category AS gc
     LEFT JOIN guide AS g 
            ON g.id_guide = gc.id_guide
         WHERE g.title IS NULL

  )