Question

I need to delete record from ent table that does not exist in both column of ent_id or ent_id_val in table value

ent

+--------+
| ent_id |
+--------+
|      1 |
|      2 |
|      3 |
+--------+

value

+--------+------------+
| ent_id | ent_id_val |
+--------+------------+
|      1 |       NULL |
|   NULL |          2 |
+--------+------------+

The ent_id can be in either colum of ent_id and ent_id_val in value table.
In the example above, I want the record ent_id = 3 to be deleted.
Below is what I have attempt, it does delete some, but I wonder why it does not delete all completely ? I still have record in ent table that is not being used in value table.

DELETE e.* 
FROM ent e 
LEFT JOIN value v1 on e.ent_id = v1.ent_id 
LEFT JOIN value v2 on v2.ent_id_val = e.ent_id
WHERE v1.ent_id is null and v2.ent_id_val is null

Answer 1

DELETE a  
FROM  ent a
      LEFT JOIN value b
         ON   a.ent_ID = b.ent_ID
      LEFT JOIN value c
         ON   a.ent_ID = c.ent_id_val
WHERE b.ent_ID IS NULL AND c.ent_id_val IS NULL;

• See SQLFiddle Demo

OR

DELETE a FROM ent a
        LEFT JOIN 
        (
            SELECT ent_ID FROM value
            UNION
            SELECT ent_id_val AS ent_ID FROM value
        ) b ON a.ent_ID = b.ent_ID
WHERE   b.ent_ID IS NULL

• See SQLFiddle Demo