Results for IN and EXISTS

Question

I have two table Table_hold and table_pass and I am using the following query to find out if any id in Table_pass exists, then delete the same from Table_hold. I am using below query:

delete from Table_hold
        where  EXISTS ( SELECT 1 FROM Table_pass pass
            WHERE id = pass.id );

Is there something wrong with this query? Even though there is Id=4 in table_hold and it's not there in table_pass, it still it got deleted from table_hold.

Below are the dummy tables I created:

create table Table_pass(id1 number);
create table table_hold(id1 number);

insert into table_pass values(1);
insert into table_pass values(2);
insert into table_pass values(3);
insert into table_hold values(4);


 delete from Table_hold
 where  EXISTS ( SELECT 1 FROM Table_pass pass
 WHERE id1 = pass.id1 );

This query deletes one row with ID 4 in table_hold.

Answer 1

Qualify all column references!

delete from Table_hold
    where exists (select 1
                  from Table_pass p
                  where p.id = table_hold.id
                 );

This subquery:

where EXISTS (SELECT 1
              FROM Table_pass pass
              WHERE id = pass.id
             );

has a reference to id. How is it resolved? Well, from the inside out. So this is equivalent to:

where EXISTS (SELECT 1
              FROM Table_pass pass
              WHERE pass.id = pass.id
--------------------^ NOT table_hold
             );

The solution is to get in the habit of qualifying all column names.