Complex SQL View with Joins & Where clause - sql

Question

My SQL skill level is pretty basic. I have certainly written some general queries and done some very generic views. But once we get into joins, I am choking to get the results that I want, in the view I am creating.
I feel like I am almost there. Just can't get the final piece
SELECT dbo.ics_supplies.supplies_id,
dbo.ics_supplies.old_itemid,
dbo.ics_supplies.itemdescription,
dbo.ics_supplies.onhand,
dbo.ics_supplies.reorderlevel,
dbo.ics_supplies.reorderamt,
dbo.ics_supplies.unitmeasure,
dbo.ics_supplies.supplylocation,
dbo.ics_supplies.invtype,
dbo.ics_supplies.discontinued,
dbo.ics_supplies.supply,
dbo.ics_transactions.requsitionnumber,
dbo.ics_transactions.openclosed,
dbo.ics_transactions.transtype,
dbo.ics_transactions.originaldate
FROM dbo.ics_supplies
LEFT OUTER JOIN dbo.ics_orders
ON dbo.ics_supplies.supplies_id = dbo.ics_orders.suppliesid
LEFT OUTER JOIN dbo.ics_transactions
ON dbo.ics_orders.requisitionnumber =
dbo.ics_transactions.requsitionnumber
WHERE ( dbo.ics_transactions.transtype = 'PO' )
When I don't include the WHERE clause, I get 17,000+ records in my view. That is not correct. It's doing this because we are matching on a 1 to many table. Supplies table is 12,000 records. There should always be 12,000 records. Never more. Never less.
The pieces that I am missing are:
I only need ONE matching record from the ICS_Transactions Table. Ideally, the one that I want is the most current 'ICS_Transactions.OriginalDate'.
I only want the ICS_Transactions Table fields to populate IF ICS_Transacions.Type = 'PO'. Otherwise, these fields should remain null.
Sample code or anything would help a lot. I have done a lot of research on joins and it's still very confusing to get what I need for results.
EDIT/Update
I feel as if I asked my question in the wrong way, or didn't give a good overall view of what I am asking. For that, I apologize. I am still very new to SQL, but trying hard.
ICS_Supplies Table has 12,810 records
ICS_Orders Table has 3,666 records
ICS_Transaction Table has 4,701 records
In short, I expect to see a result of 12,810 records. No more and no less. I am trying to create a View of ALL records from the ICS_Supplies table.
Not all records in Supply Table are in Orders and or Transaction Table. But still, I want to see all 12,810 records, regardless.
My users have requested that IF any of these supplies have an open PO (ICS_Transactions.OpenClosed = 'Open' and ICS_Transactions.InvType = 'PO') Then, I also want to see additional fields from ICS_Transactions (ICS_Transactions.OpenClosed, ICS_Transactions.InvType, ICS_Transactions.OriginalDate, ICS_Transactions.RequsitionNumber).
If there are no open PO's for supply record, then these additional fields should be blank/null (regardless to what data is in these added fields, they should display null if they don't meet the criteria).
The ICS_Orders Table is nly needed to hop from the ICS_Supplies to the ICS_Transactions (I first, need to obtain the Requisition Number from the Orders field, if there is one).
I am sorry if I am not doing a good job to explain this. Please ask if you need clarification.

Answer 1

Here's a simplified version of Ross Bush's answer (It removes a join from the CTE to keep things more focussed, speed things up, and cut down the code).
;WITH
ordered_ics_transactions AS
(
SELECT
*,
ROW_NUMBER() OVER (PARTITION BY requisitionnumber
ORDER BY originaldate DESC
)
AS seq_id
FROM
dbo.ics_transactions
)
SELECT
s.supplies_id, s.old_itemid,
s.itemdescription, s.onhand,
s.reorderlevel, s.reorderamt,
s.unitmeasure, s.supplylocation,
s.invtype, s.discontinued,
s.supply,
t.requsitionnumber, t.openclosed,
t.transtype, t.originaldate
FROM
dbo.ics_supplies AS s
LEFT OUTER JOIN
dbo.ics_orders AS o
ON o.supplies_id = s.suppliesid
LEFT OUTER JOIN
ordered_ics_transactions AS t
ON t.requisitionnumber = o.requisitionnumber
AND t.transtype = 'PO'
AND t.seq_id = 1
This will only join the most recent transaction record for each requisitionnumber, and only if it has transtype = 'PO'
IF you want to reverse that (joining only transaction records that have transtype = 'PO', and of those only the most recent one), then move the transtype = 'PO' filter to be a WHERE clause inside the ordered_ics_transactions CTE.

Answer 2

You can possibly work with the query below to get what you need.
1. I only need ONE matching record from the ICS_Transactions Table. Ideally, the one that I want is the most current 'ICS_Transactions.OriginalDate'.
I would solve this by creating a CTE with all the ICS_Transaction fields needed in the query, rank-ordered by OPriginalDate, partitioned by suppliesid.
2. I only want the ICS_Transactions Table fields to populate IF ICS_Transacions.Type = 'PO'. Otherwise, these fields should remain null.
If you move the condition from the WHERE clause to the LEFT JOIN then ICS_Transactions not matching the criteria will be peeled and replaced with null values with the rest of the query records.
;
WITH ReqNumberRanked AS
(
SELECT
dbo.ICS_Orders.SuppliesID,
dbo.ICS_Transactions.RequisitionNumber,
dbo.ICS_Transactions.TransType,
dbo.ICS_Transactions.OriginalDate,
dbo.ICS_Transactions.OpenClosed,
RequisitionNumberRankReversed = RANK() OVER(PARTITION BY dbo.ICS_Orders.SuppliesID, dbo.ICS_Transactions.RequisitionNumber ORDER BY dbo.ICS_Transactions.OriginalDate DESC)
FROM
dbo.ICS_Orders
LEFT OUTER JOIN dbo.ICS_Transactions ON dbo.ICS_Orders.RequisitionNumber = dbo.ICS_Transactions.RequsitionNumber
)
SELECT
dbo.ICS_Supplies.Supplies_ID, dbo.ICS_Supplies.Old_ItemID,
dbo.ICS_Supplies.ItemDescription, dbo.ICS_Supplies.OnHand,
dbo.ICS_Supplies.ReorderLevel, dbo.ICS_Supplies.ReorderAmt,
dbo.ICS_Supplies.UnitMeasure,
dbo.ICS_Supplies.SupplyLocation, dbo.ICS_Supplies.InvType,
dbo.ICS_Supplies.Discontinued, dbo.ICS_Supplies.Supply,
ReqNumberRanked.RequsitionNumber,
ReqNumberRanked.OpenClosed,
ReqNumberRanked.TransType,
ReqNumberRanked.OriginalDate
FROM
dbo.ICS_Supplies
LEFT OUTER JOIN dbo.ICS_Orders ON dbo.ICS_Supplies.Supplies_ID = dbo.ICS_Orders.SuppliesID
LEFT OUTER JOIN ReqNumberRanked ON ReqNumberRanked.RequisitionNumber = dbo.ICS_Transactions.RequsitionNumber
AND (ReqNumberRanked.TransType = 'PO')
AND ReqNumberRanked.RequisitionNumberRankReversed = 1