Question

I have 3 tables, the first one, table1, has as primary key the id column, the second table (table2) has a column table1_id that refer as foreign key to the table1.id, the third table (table3) has, as table2, a column table1_id that refer as foreign key to table1.id.

I have to delete from table1 all the rows where table1.id is not in table2.table1_id and not in table3.table1_id

now i am using this query:

DELETE FROM table1
WHERE  table1.id IN (SELECT table1.id
                     FROM   (table2
                             RIGHT OUTER JOIN table1
                               ON table2.table1_id = table1.id)
                            LEFT OUTER JOIN table3
                              ON table3.table1_id = table1.id
                     WHERE  table2.table1_id IS NULL
                            AND table3.table1_id IS NULL);  

but it is very slow, it takes a lot of time, there are some better approach to this delete statement?

If this can help i can assume that table2 has more data that table3.

The database i am using is Apache Derby.

Thanks for the help.

Answer 1

Assuming you got the obvious covered (indices created for table1.id, table2.table1_id and table3.table1_id), you don’t need to perform full outer joins just to test if a key is in another table, you can use subqueries and exists() — or not exists() in your case.

And since you’re only testing for existence, you can use the following pattern:

where not exists ( select top 1 1 from... where... )