SQL Server - Auto-incrementation that allows UPDATE statements

Question

When adding an item in my database, I need it to auto-determine the value for the field DisplayOrder. Identity (auto-increment) would be an ideal solution, but I need to be

Answer 1

You way works fine (with a little modification) and is simple. I would wrap it in a transaction like @David Knell said. This would result in code like:

CREATE PROCEDURE [dbo].[AddItem]

AS

DECLARE @DisplayOrder INT

BEGIN TRANSACTION

SET @DisplayOrder = (SELECT MAX(DisplayOrder) FROM [dbo].[MyTable]) + 1

INSERT INTO [dbo].[MyTable] ( DisplayOrder ) VALUES ( @DisplayOrder )

COMMIT TRANSACTION

Wrapping your SELECT & INSERT in a transaction guarantees that your DisplayOrder values won't be duplicated by AddItem. If you are doing a lot of simultaneous adding (many per second), there may be contention on MyTable but for occasional inserts it won't be a problem.