Distinct Values in SQL Query - Advanced - sql

Question

I have searched high and low and have tried for hours to manipulate the various other queries that seemed to fit but I've had no joy.
I have several Tables in Microsoft SQL Server 2005 that I'm trying to join, an example of which is:
Company Table (Comp_CompanyId, Comp_Name)
GroupCode_Link Table (gcl_c_groupcodelinkid, gcl_c_groupcodeid, gcl_c_companyid)
GroupCode Table (grp_c_groupcodeid, grp_c_groupcode, grp_c_name)
ItemCode Table (itm_c_itemcodeid, itm_c_name, itm_c_itemcode, itm_c_group)
ItemCode_Link Table (icl_c_itemcodelinkid, icl_c_companyid, icl_c_groupcodeid, icl_c_itemcodeid)
I'm using Link Tables to associate a Group to a Company, and an Item to a Group, so a Company could have multiple groups, with multiple items in each group.
Now, I'm trying to create an Advanced Find Function that will allow a user to enter, for example, an Item Code and the result should display those companies that have that item, sounds nice and simple!
However, I haven't done something right, if I use the following query ' if the company has this item OR this item, display it's name', I get the company appearing twice in the result set, once for each item.
What I need is to be able to say is:
"Show me a list of companies that have these items (displaying each company only once!)"
I've had a go at using COUNT, DISTINCT and HAVING but have failed on each as my query knowledge isn't up to it!

Answer 1

First, from your description it sounds like you might have a problem with your E-R (entity-relationship) model. Your description tells me that your E-R model looks something like this:
Associative entities (CompanyGroup, GroupItem) exist to implement many-to-many relationships (since many-to-many isn't supported directly by relational databases).
Nothing wrong with that if a group can exist within multiple companies or an item across multiple groups. It would seem more likely that, at least, each group is specific to a company (I can see items existing across multiple companies and/or groups: more than one company retails, for instance, Cuisinart food processors). If that is the case, a better E-R model would be to make each group a dependent entity with a CompanyID that is a component of its primary key. It's a dependent entity because the group doesn't have an independent existence: it's created by/on behalf of and exists for its parent company. If the company goes away, the group(s) tied to it go away. No your E-R model looks like this:
From that, we can write the query you need:
select *
from Company c
where exists ( select *
from GroupItem gi
where gi.ItemID in ( desired-itemid-1 , ... , desired-itemid-n )
and gi.CompanyID = c.CompanyID
)
As you can see, dependent entities are a powerful thing. Because of the key propagation, queries tend to get simpler. With the original data model, the query would be somewhat more complex:
select *
from Company c
where exists ( select *
from CompanyGroup cg
join GroupItem gi on gi.GroupId = cg.GroupID
where gi.ItemID in ( desired-itemid-1 , ... , desired-itemid-n )
and cg.CompanyID = c.CompanyID
)
Cheers!

Answer 2

SELECT *
FROM company c
WHERE (
SELECT COUNT(DISTINCT icl_c_itemcodeid)
FROM GroupCode_Link gl
JOIN ItemCode_Link il
ON il.icl_c_groupcodeid = gcl_c_groupcodeid
WHERE gl.gcl_c_companyid = c.Comp_CompanyId
AND icl_c_companyid = c.Comp_CompanyId
AND icl_c_itemcodeid IN (#Item1, #Item2)
) >= 2
Replace >= 2 with >= 1 if you want "any item" instead of "all items".

Answer 3

If you need to show companies that have item1 AND item2, you can use Quassnoi's answer.
If you need to show companies that have item1 OR item2, then you can use this:
SELECT
*
FROM
company
WHERE EXISTS
(
SELECT
icl_c_itemcodeid
FROM
GroupCode_Link
INNER JOIN
ItemCode_Link
ON icl_c_groupcodeid = gcl_c_groupcodeid
AND icl_c_itemcodeid IN (#item1, #item2)
WHERE
gcl_c_companyid = company.Comp_CompanyId
AND
icl_c_companyid = company.Comp_CompanyId
)

Answer 4

I would write something like the code below:
SELECT
c.Comp_Name
FROM
Company AS c
WHERE
EXISTS (
SELECT
1
FROM
GroupCode_Link AS gcl
JOIN
ItemCode_Link AS icl
ON
gcl.gcl_c_groupcodeid = icl.icl_c_groupcodeid
JOIN
ItemCode AS itm
ON
icl.icl_c_itemcodeid = itm.itm_c_itemcodeid
WHERE
c.Comp_CompanyId = gcl.gcl_c_companyid
AND
itm.itm_c_itemcode IN (...) /* here provide list of one or more Item Codes to look for */
);
but I see there's a icl_c_companyid column in the ItemCode_Link so using GroupCode_Link table is not necessary?