Obtain maximum row_number inside a cross apply

Question

I am having trouble in calculating the maximum of a row_number in my sql case.

I will explain it directly on the SQL Fiddle example, as I think it will be faster to understand: SQL Fiddle

• Columns 'OrderNumber', 'HourMinute' and 'Code' are just to represent my table and hence, should not be relevant for coding purposes
• Column 'DateOnly' contains the dates
• Column 'Phone' contains the phones of my customers
• Column 'Purchases' contains the number of times customers have bought in the last 12 months. Note that this value is provided for each date, so the 12 months time period is relative to the date we're evaluating.

Finally, the column I am trying to produce is the 'PREVIOUSPURCHASES' which counts the number of times the figure provided in the column 'Purchases' has appeared in the previous 12 months (for each phone).

You can see on the SQL Fiddle example what I have achieved so far. The column 'PREVIOUSPURCHASES' is producing what I want, however, it is also producing lower values (e.g. only the maximum one is the one I need).

For instance, you can see that rows 4 and 5 are duplicated, one with a 'PREVIOUSPURCHASES' of 1 and the other with 2. I don't want to have the 4th row, in this case.

I have though about replacing the row_number by something like max(row_number) but I haven't been able to produce it (already looked at similar posts at stackoverflow...).

This should be implemented in SQL Server 2012.

Thanks in advance.

Answer 1

I'm not sure what kind of result set you want to see but is there anything wrong with what's returned with this?

SELECT c.OrderNumber, c.DateOnly, c.HourMinute, c.Code, c.Phone, c.Purchases, MAX(o.PreviousPurchases)
FROM cte c CROSS APPLY (
                      SELECT t2.DateOnly, t2.Phone,t2.ordernumber, t2.Purchases, ROW_NUMBER() OVER(PARTITION BY c.DateOnly ORDER BY t2.DateOnly) AS PreviousPurchases
                      FROM CurrentCustomers_v2 t2
                      WHERE c.Phone = t2.Phone AND t2.purchases<=c.purchases AND DATEDIFF(DAY, t2.DateOnly, c.DateOnly) BETWEEN 0 AND 365
                      ) o
WHERE c.OrderNumber = o.OrderNumber
GROUP BY c.OrderNumber, c.DateOnly, c.HourMinute, c.Code, c.Phone, c.Purchases
ORDER BY c.DateOnly