Question

I have a table with an Identity column which provides my ticketNumber.

I want another table to provide a ticketStepNumber. A ticket may have 0 or more steps, so I won’t always be creating a ticketStepNumber.

The ticketStepNumber value is a combination of the ticketNumber column (int) and the stepNumber column (int). I’d like to define the stepNumber column like an identity but starting at 1 for each value of the ticketNumber column, so all I have to do in my stored procedure is pass in a ticketNumber and I’ll get the new stepNumber. E.g.

ticketNumber  stepNumber
1             1
2             1
2             2
2             3
4             1
7             1
7             2

Is there a way to define this in the table definition or do I have to do it in the SP?

Answer 1

No, there’s no such thing in SQL Server, sorry. An IDENTITY column is a single, ever-increasing column – there’s no basing that number on the values of another column.

If you really must have a sequential number for each step, then you’ll have to handle the assignments (and make sure it’s truly unique) yourself.

UPDATE: if you have some other column in your table that could serve as a sort expression, you could use the ROW_NUMBER function to achieve what you want; e.g. if you had a TicketDate (DATETIME) column, you could do something like:

SELECT 
   TicketNUmber, 
   ROW_NUMBER() OVER (PARTITION BY TicketNumber ORDER BY TicketDate) AS StepNumber
FROM YourTable

This would “partition” your data by TicketNumber (e.g. start counting at 1 for each of the values in the partition) and then use the ROW_NUMBER to sequentially number the rows, based on the TicketDate for ordering.

Marc