SQL查询用于查找表中没有的结果

Question

I am a little bit rusty on my SQL and would like some help with these queries that I am struggling getting my head round or even finding out if it is possible.

Hi so I have some tables;

clients,products,clientproducts

when a client opts in for a product that is added to clientproducts, using the clientid and the productid.

the easy query I want to run a query that will only show me products the client has opted in for.

the harder one I also want to run a query that will show me just the clients that haven't opted in for a product/s.

Thank you for your help in advance.

Answer 1

Query 1:

   SELECT table1.id1 FROM table1
    WHERE table1.id1 IN (SELECT table2.foreign_id FROM table2);

Query 2:

      SELECT table1.id1 FROM table1
        WHERE table1.id1 NOT IN (SELECT table2.foreign_id FROM table2);