How to get previous owner in sql table? - sql

Question

I have a Transaction table (transId, sn, customerId, date) that lists item transactions between customers. Some item has sn (serial number) and travels from one customer to another. For some customer (12345678), I need to find out who was the last previous owner of customer's items.
Here's my query:
SELECT c.*,
p.transId,
p.customerId
FROM Transaction c
LEFT JOIN Transaction p ON c.sn = p.sn
WHERE p.transId = (SELECT MAX(t.transId)
FROM Transaction t
WHERE t.transId < c.transId
AND t.sn = c.sn)
AND c.customerId = 12345678
ORDER BY p.transId;
This query works fine except when item has no previous owner. Should return nulls for p.transId and p.customerId but insead it returns 0 rows. Database is Access.
UPDATE: I need to have BOTH current owner and previous owner in result (in one row). And, it should work for middle owners (like a log; if the customer is not current owner, but was a owner before).
UPDATE: For certain customer (that would be passed as a parameter; in our case customerId=12345678), I need to see the list of all items that he ever owned and the last previous owner of the items (from which customer he got the item).
Some more explanations:
transId is a primary key and autonumber (identity) - previous owner will have smaller transId than the newer owner
customerId in transaction is the buyer (new owner after that transaction)
date does not contain time; only date (should not be used in comparisons or ordering since some item can change two owners in one day)
Here is a little example that will make things more clearer (date not shown):
transaction table
-----------------------
|transId|sn|customerId|
| 1| 1| 12345678|
| 2| 2| 87654321|
| 3| 2| 12345678|
| 4| 2| 11223344|
| 5| 2| 12345678|
-----------------------
for customerId=12345678 result should be
result
--------------------------------------------------
|transId|sn|customerId|prevTransId|prevCustomerId|
| 1| 1| 12345678| NULL| NULL|
| 3| 2| 12345678| 2| 87654321|
| 5| 2| 12345678| 4| 11223344|
--------------------------------------------------

Answer 1

Move condition of p.transId = ... from WHERE clause into a JOIN condition (and you do not need c.sn = p.sn in any case):
Normal SQL:
SELECT c.*,
p.transId,
p.customerId
FROM Transaction c
LEFT JOIN Transaction p
ON p.transId = (SELECT MAX(t.transId)
FROM Transaction t
WHERE t.transId < c.transId
AND t.sn = c.sn)
WHERE c.customerId = 12345678
ORDER BY p.transId;
MS Access SQL:
SELECT c.*,
p.transId,
p.customerId
FROM Transaction c
LEFT JOIN ((SELECT t.transId, MAX(z.transId) AS PrevTransId
FROM Transaction t
LEFT JOIN Transaction z on t.sn = z.sn
WHERE z.transId < t.transId
GROUP BY t.transId) x
LEFT JOIN Transaction p ON p.TransId = x.PrevTransId
) ON x.TransId = c.TransId
WHERE c.customerId = 12345678
ORDER BY p.transId;