How to get the next number in a sequence

Question

I have a table like this:

+----+-----------+------+-------+--+
| id | Part      | Seq  | Model |  |
+----+-----------+------+-------+--+
| 1  | Head      | 0         


        

Answer 1

I would not try to store the Seq value in the table in the first place.

As you said in the comments, your ID is IDENTITY, which increases automatically in a very efficient and concurrent-safe way by the server. Use it for determining the order in which rows were inserted and the order in which the Seq values should be generated.

Then use ROW_NUMBER to generate values of Seq partitioned by Model (the sequence restarts from 1 for each value of Model) as needed in the query.

SELECT
    ID
    ,Part
    ,Model
    ,ROW_NUMBER() OVER(PARTITION BY Model ORDER BY ID) AS Seq
FROM YourTable