Question

I have a database table called ‘members‘. Assigned to members is a position.

Positions come from Departments. I have Departments, then Sub-Departments within those and Positions within the Sub-Departments.

Hopefully I haven’t lost you.

What I want to do is is select all the members within a department, excluding any of those members from one position within that department.

“departments” Table: (includes departments and sub-departments)

ID     NAME                  PARENT_ID
1      Department #1         NULL
2      Department #2         NULL
3      Sub Department #1     1       
4      Sub Department #2     1       
5      Sub Department #3     2   

“departments_positions” Table:

ID     NAME             SUB_DEPARTMENT_ID
1      Position #1      3
2      Position #2      3
3      Position #3      4    

“members_positions” Table:

ID     MEMBER_ID     POSITION_ID
1      1             1
2      1             2
3      1             3         

Here’s my MySQL code:

SELECT m.* FROM members AS m 
    LEFT JOIN members_positions AS mp ON mp.member_id = m.id
    LEFT JOIN departments_positions AS dp ON mp.position_id = dp.id
    LEFT JOIN departments AS sd ON dp.sub_department_id = sd.id
    LEFT JOIN departments AS d ON sd.parent_id = d.id
    WHERE mp.position_id != '2' AND d.id = '1'
    GROUP BY m.id

So as you can see I want to extract the members that are in “Department #1” (ID: 1 from departments_table) but not members who are in Position #2 (ID: 2 from departments_positions table) of that department.

Hopefully I am making sense. My code above doesn’t seem to work. It just exports everyone from the department.

Answer 1

It’s because you are using LEFT JOIN, which will not filter data.

Change your query to use INNER JOIN.

You also cannot use a select * if you’re grouping by member id.

Edit: I inputed your tables into a local mysql db and confirmed this query working.

SELECT DISTINCT mp.member_id
FROM        members_positions mp
INNER JOIN  departments_positions dp ON dp.id = mp.position_id
    AND     mp.position_id != 2
INNER JOIN  departments sd on sd.id = dp.sub_department_id
    AND     sd.parent_id = 1
GROUP BY    mp.member_id

Also, any reason why you’re quoting your int values 2 & 1 in the where statement?

If you only want the unique member id’s, you don’t need to do a GROUP BY. You should switch your select to this and then use an outer select to get all the member info:

SELECT m.* 
FROM members m
INNER JOIN (
    SELECT DISTINCT mp.member_id
    ... the rest...
) innerQ ON innerQ.member_id = m.id