Question

Table 1:

• id
• name

Table 2:

• id
• other_table_id
• table_1_id
• ..

Basically what I want to do is

Delete from table_1 
where id not in (select table_1_id 
                 from table_2 
                 group by table_1_id);

Which should work, what I am wondering is if the sub query is the best way to do this/ is there any other way?

Answer 1

I prefer to use JOIN over subquery.

DELETE a FROM table_a a
            LEFT JOIN table_2 b
                ON a.ID = b.table_1_id
WHERE   b.table_1_id IS NULL

• SEE SQLFiddle Demo