Why can't I exclude this row based on a condition? - mysql

Question

http://sqlfiddle.com/#!3/3ec1f/119
Here's my fiddle...I want the result to look like this but the query I'm using doesn't do that:
My problem with the query is that I can't seem to exclude "The Kingdom of the Crystal Skull" using the exclusion_flag condition. I also don't know why it seems that Contract 3 (Raiders of the Lost Arc) is not showing up either. I have been toiling with this for hours and have no idea what the problem is. I tried looking into subqueries, but I'm not sure that's the solution...

Answer 1

There's a couple of questions/issues there so I'll try to address them individually.
1) You can't exclude "The Kingdom of the Crystal Skull" using the exclusion_flag because contract_sid 7 and 8 both refer to product_list_sid 3 which includes "The Kingdom of the Crystal Skull" - you would need to create a separate product_list_sid if you wanted a contract which excluded it.
2) "Raiders of the Lost Arc" (contract_sid 3) isn't showing up because it's a "single product" contract, and your query only joins from scope to product_list_join using product_list_id - contract_sid 3 is in the product_sid column so you need a separate join to cater for contracts that use product_sid instead of product_list_sid (I assume that a contract can't use both). This is a pretty dodgy schema design but here's a query that solves that issue. Notice the use of LEFT OUTER JOIN to indicate that the table being joined to might not contain any rows (for example when scope.product_list_sid is NULL but scope.product_sid is not).
SELECT s.contract_sid,
c.contract_description,
ISNULL(p.product_description, p2.product_description) AS product_description
FROM scope s
JOIN contracts c ON (c.contract_sid = s.contract_sid)
LEFT OUTER JOIN
product_list_join plj ON (plj.product_list_sid = s.product_list_sid)
LEFT OUTER JOIN
products p ON (p.product_sid = plj.product_sid)
LEFT OUTER JOIN
products p2 ON (p2.product_sid = s.product_sid)
WHERE s.exclusion_flag = 'N'
ORDER BY s.contract_sid;
Here's the SQLFiddle for my solution: http://sqlfiddle.com/#!3/fc62e/10
Edit: After posting this I realised what you're actually trying to do - the scope table not only provides the details of contracts but also provides specific products to exclude from contracts. Again, this is bad schema design and there should be a separate scope_exclusions table or something, but here's a query that does that and excludes "The Kingdom of the Crystal Skull" as requested:
SELECT inner_query.contract_description,
inner_query.product_description
FROM (
SELECT s.contract_sid,
c.contract_description,
ISNULL(p.product_sid, p2.product_sid) AS product_sid,
ISNULL(p.product_description, p2.product_description) AS product_description
FROM scope s
JOIN contracts c ON (c.contract_sid = s.contract_sid)
LEFT OUTER JOIN
product_list_join plj ON (plj.product_list_sid = s.product_list_sid)
LEFT OUTER JOIN
products p ON (p.product_sid = plj.product_sid)
LEFT OUTER JOIN
products p2 ON (p2.product_sid = s.product_sid)
WHERE s.exclusion_flag = 'N'
) inner_query
WHERE NOT EXISTS ( SELECT 1
FROM scope
WHERE exclusion_flag = 'Y'
AND contract_sid = inner_query.contract_sid
AND product_sid = inner_query.product_sid )
ORDER BY inner_query.contract_description;
SQL Fiddle: http://sqlfiddle.com/#!3/fc62e/14