Find missing values in third table based on two other tables

Question

Hi- I have tried to do this on my own but the answer eludes me. Can someone please point me in a better direction? We have a table project_categories with project_IDs and related project category_IDs. We have another table contact_categories with contact_IDs and related contact category_IDs. We use these two tables to link contacts to projects by at least one category_ID. It works well for email notifications. We have a third table for "planholders" who are interested in particular projects. The planholder table has contact_IDs and related project_IDs. I want to find contacts who have expressed interest in a project, by inserting a row in the planholder table, but they have not selected any of the project categories in contact categories. This would be an unusually rare exception, so to test it I added myself as a contact 100010 and as a project "planholder", but deliberately did not select any of the related project categories in contact categories.
select ph.contact_id, ph.project_id, pc.category_id, cc.category_id
from purchasing_planholder ph, purchasing_project_categories pc, purchasing_contact_categories cc
where ph.project_id=pc.project_id
and ph.contact_id=cc.contact_id
and ph.contact_id||ph.project_id||cc.category_id
not in (select ph.contact_id||pc.project_id||pc.category_id
from purchasing_planholder ph, purchasing_project_categories pc, purchasing_contact_categories cc
where ph.project_id=pc.project_id
and ph.contact_id=cc.contact_id)
and ph.contact_id=100010
This gives me every category for the test contact and every category for the project. I want to find contacts in the planholder table who have not selected any of the categories related to the specific project they selected in the planholder table. I tried minus, outer joins, etc. Does this require PL/SQL and a temp table, or can I find the exceptions with a report? Or do I need a different approach? The ideal answer would display one row with the contact_ID and the project_ID, where the contact has not selected any of the project categories. This would be used to alert them that they need to select at least one of the project categories on the contact form. Thanks for any feedback.
Peter
CONTACT_ID PROJECT_ID CATEGORY_ID CATEGORY_ID
100010 701 1 19
100010 701 1 18
100010 701 16 19
100010 701 16 18
100010 701 21 19
100010 701 21 18
100010 701 24 19
100010 701 24 18
8 rows selected

Answer 1

Hi User,
When you Post a Question in Forum, Please be clear of the Inputs to be given, the expected output and the tries you made,
the errors/results you faced.
Also, see this link of BluShadow.
SQL and PL/SQL FAQ
Please enclose the query or programs in code tags for a formatted code.
Just Try something like this,
SELECT *
  FROM emp c
WHERE NOT EXISTS (SELECT *
                     FROM emp a
                    WHERE EXISTS (SELECT *
                                    FROM emp b
                                   WHERE a.empno = b.empno));In the Inner Query, the conditon checked is empno same in both the tables, and for example some rows are obtained, other than
this rows all other results are obtained from the outer query.
In the above case no rows are returned.
Thanks,
Shankar