Question

I have two tables, let’s call them table1 and table2. They both have a column called ID1 and ID2 which are respective PK for each of two tables.

I have also another table, called table3 which contains ID1 and ID2, establishing a many to many relation between these two tables.

What I need is to get all the records from table2 that are not related with records in table1.

Ex.

• Table 1 contains a record with ID = 1
• Table 2 contains two records with ID 1, 2
• Table 3 contains one record with values 1 – 1

I need a query that will give me as result 2.

Can anyone suggest me a way to proceed?

Thanks

Answer 1

SELECT t2.ID2
    FROM table2 t2
    WHERE NOT EXISTS(SELECT NULL
                         FROM table3 t3
                         WHERE t3.ID2 = t2.ID2);

You could also use a LEFT JOIN:

SELECT t2.ID2
    FROM table2 t2
        LEFT JOIN table3 t3
            ON t2.ID2 = t3.ID2
    WHERE t3.ID2 IS NULL;