Using a trigger to simulate a second identity column in SQL Server 2005

Question

I have various reasons for needing to implement, in addition to the identity column PK, a second, concurrency safe, auto-incrementing column in a SQL Server 2005 database.

Answer 1

A solution to this issue from "Inside Microsoft SQL Server 2008: T-SQL Querying" is to create another table with a single row that holds the current max value.

CREATE TABLE dbo.Sequence(
 val int 
 )

Then to allocate a range of sufficient size for your insert

CREATE PROC dbo.GetSequence
@val AS int OUTPUT,
@n as int =1
AS
UPDATE dbo.Sequence 
SET @val = val = val + @n;

SET @val = @val - @n + 1; 

This will block other concurrent attempts to increment the sequence until the first transaction commits.

For a non blocking solution that doesn't handle multi row inserts see my answer here.