MySQL select rows where left join is null

Question

I have these MySQL tables:

table1:

id | writer
1  | Bob   
2  | Marley
3  | Michael

table2:

user_one | user_two
            


        

Answer 1

One of the best approach if you do not want to return any columns from table2 is to use the NOT EXISTS

SELECT  table1.id 
FROM    table1 T1
WHERE
  NOT EXISTS (SELECT *
              FROM table2 T2
              WHERE T1.id = T2.user_one
                  OR T1.id = T2.user_two)

Semantically this says what you want to query: Select every row where there is no matching record in the second table.

MySQL is optimized for EXISTS: It returns as soon as it finds the first matching record.