SQL Microsoft Access

Question

I have a table of transactions in Microsoft Access that contains many transactions for many vendors. I need to identify if there is sequential transaction numbering for each vendor. I don't know what the sequence will be or the number of transactions per vendor. I need to write a SQL that identifies sequential numbering for vendors and sets a field to '1' if present. I was thinking of running nested loops that first determine number of transactions per vendor then loops through those transactions comparing the transaction numbers. Can anybody help me with this??

Answer 1

To find one sequential set (2 records where one transaction number follows the other):

SELECT transactionId FROM tbl WHERE EXISTS 
  (SELECT * FROM tbl as t WHERE tbl.vendorId = t.vendorId 
   AND tbl.transactionId+1 = t.transactionId)

Answer 2

I would use a query that finds gaps in numbering for any vendor, and if that returns any records, then you do not have sequential numbering for all vendors.

SELECT *
FROM tblTransaction As T1
WHERE (
    SELECT TOP 1 T2.transactionID
    FROM tblTransaction As T2
    WHERE T1.vendorID = T2.vendorID AND
          T1.transactionID < T2.transactionID
    ORDER BY T2.transactionID
) - T1.transactionID > 1

What this does is, for each record in the table, look for the lowest-numbered other transactionID in the same table that is for the same vendor and has a higher-numbered transactionID than the first one. If that the transactionID value of that record is more than one higher than the value in the first record, that represents a gap in numbering for the vendor.

Edit: Changed variable names above as requested.

Answer 3

I'm not sure this is the most straightforward approach but I think it could work. Apologies for using multiple steps but Jet 4.0 kind of forces one to do so.**

I've assumed all transactionId values are positive integers and that a sequence is a set of evenly spaced transactionId values by vendorId . I further assume there is a key on (vendorId, transactionId) .

First step, elmininate invalid rows eg need at least three rows to be able to determine a sequence (do all other rows pass or fail?); may want to filter other junk out here too (eg rows/groups with NULL values):

CREATE VIEW tbl1
AS
SELECT T1.vendorId, T1.transactionId
  FROM tbl AS T1
 WHERE EXISTS (
               SELECT T2.vendorId
                 FROM tbl AS T2
                WHERE T2.vendorId = T1.vendorId
                GROUP 
                   BY T2.vendorId
                HAVING COUNT(*) > 2
              );

Find the lowest value for each vendor (comes in handy later):

CREATE VIEW tbl2
AS
SELECT vendorId, MIN(transactionId) AS transactionId_min
  FROM tbl1
 GROUP 
    BY vendorId;

Make all sequences start at zero ( transactionId_base_zero ) by subtracting the lowest value for each vendor:

CREATE VIEW tbl3
AS
SELECT T1.vendorId, T1.transactionId, 
       T1.transactionId - T2.transactionId_min AS transactionId_base_zero
  FROM tbl1 AS T1
       INNER JOIN tbl2 AS T2
          ON T1.vendorId = T2.vendorId;

Predict the step value (difference between adjacent sequence values) based on the MAX , MIN and COUNT set values for each vendor:

CREATE VIEW tbl4
AS
SELECT vendorId, 
       MAX(transactionId_base_zero) / (COUNT(*) - 1)
          AS transactionId_predicted_step
  FROM tbl3;

Test that the predicted step value hold true for each squence value ie (pseudo code) this_transactionId - step_value = prior_transactionId (omit the lowest transactionId because it doesn't have a prior value!):

SELECT DISTINCT T.vendorId
  FROM tbl3 AS T
 WHERE T.transactionId_base_zero > 0
       AND NOT EXISTS (
                       SELECT *
                         FROM tbl3 AS T3
                              INNER JOIN tbl4 AS T4
                                 ON T3.vendorId = T4.vendorId      
                        WHERE T.vendorId = T3.vendorId
                              AND T.transactionId_base_zero 
                                     - T4.transactionId_predicted_step 
                                        = T3.transactionId_base_zero
                      );

The above query should return the vendorId of vendors whose transactionId values are not sequential.

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** In my defense, I ran into a couple of bugs Jet 4.0 I had to code around workaround. Yes, I do know the bugs are in Jet 4.0 (or its OLE DB provider) because a) I double checked results using SQL Server and b) they defy logic! (even SQL's own strange 3VL logic :)