Building a SQL query that doesn't include data based on hierarchy - sql

Question

I've spent quite a bit of time on Google and SO the last few days, but I can't seem to find an answer to my problem. Not knowing exactly how to phrase the issue into a reasonable question makes it a little more difficult. You don't know what you don't know, right?
Due to business limitations I can't post my exact code and database structure, so I'll do my best to give a solid example.
Customer Table - Holds customer data
[CustId] | [CustName]
---------------------
1 | John Smith
2 | Jane Doe
3 | John Doe
Code Table - Holds code data
[CodeId] | [CodeDesc]
---------------------
A | A Desc
B | B Desc
C | C Desc
D | D Desc
E | E Desc
CustomerCode Table - Combines customers with codes
[CustId] | [CodeId]
-------------------
1 | A
1 | B
2 | B
2 | C
2 | D
3 | C
3 | E
CodeHierarchy Table - Hierarchy of codes that shouldn't be included (DropCode) if a customer has a ConditionCode
[ConditionCode] | [DropCode]
----------------------------
A | B
B | C
B | D
Now I'll try to explain my actual question.
What I'm trying to accomplish is writing a query (view) that will list codes based on the CodeHierarchy table.
Results would be something like this:
[CustName] | [CodeId]
-------------------
John Smith | A
Jane Doe | B
John Doe | C
John Doe | E
Code B isn't listed for John Smith since he has code A. Codes C and D aren't listed for Jane Doe since she also has code B. John Doe has all codes listed (notice that E isn't even in the CodeHierarchy table).
I've tried a few different things (inner joins, left/right joins, subqueries, etc) but I just can't get the results I'm looking.
As a base query, this returns all codes:
SELECT
Customer.CustomerName,
Code.CodeDesc
FROM
Customer
INNER JOIN CustomerCode
ON Customer.CodeId = CustomerCode.CodeId
INNER JOIN Code
ON CustomerCode.CodeId = Code.CodeId
This only returns codes that are ConditionCodes (I understand why, but I though it might be worth a shot at the time):
SELECT
Customer.CustomerName,
Code.CodeDesc
FROM
Customer
INNER JOIN CustomerCode
ON Customer.CodeId = CustomerCode.CodeId
INNER JOIN Code
ON CustomerCode.CodeId = Code.CodeId
INNER JOIN CodeHierarchy
ON Customer.CodeId = CodeHierarchy.ConditionCode
AND Customer.CodeId != CodeHierarchy.DropCode
I tried a subquery (don't have that code available) that ended up dropping all DropCodes, regardless if a member did or did not have a qualifying hierarchy (i.e. customer rows with B weren't returned even if they didn't have A)
I had an idea of making the base query above a subquery and the joining it with the CodeHierarchy table, but I'm stuck on how to write the query:
SELECT
*
FROM
(
base query (with all codes)
) CustomerCodesAll
INNER/LEFT JOIN CodeHierarchy
ON ?
I've also been doing some reading on CTEs, but I'm not sure how I could make use of that technique.
This will end up being a view to be queried against for reporting purposes. The customer table contains much more data including dob, gender, company status, etc. The view will be straightforward and pull everything. Queries against the view will include where clauses for dob, gender, etc.
Can anyone point me in the right direction?
Thanks for any help.

Answer 1

SELECT
Customer.CustName,
Code.CodeDesc
FROM
Customer
INNER JOIN CustomerCode AS posCustomerCode
ON Customer.CustId = posCustomerCode.CustId
INNER JOIN Code
ON posCustomerCode.CodeId = Code.CodeId
LEFT JOIN CodeHierarchy
ON posCustomerCode.CodeId = CodeHierarchy.DropCode
WHERE
CodeHierarchy.ConditionCode NOT IN (
SELECT CodeId
FROM CustomerCode AS negCustomerCode
WHERE negCustomerCode.CustId=posCustomerCode.CustId
)
OR CodeHierarchy.ConditionCode IS NULL
SQLfiddle