Question

This may have been asked before, but it’s really hard to search for terms that limit the search results…

Take the following SQL snippet:

declare @source table (id int) declare @target table(id int primary key, sourceId int)   set nocount on  insert into @target values (0,0)  insert into @source(id) values(1) --insert into @source(id) values(2)  set nocount off  insert into @target select (select max(id)+1 from @target), s.id from @source s  select * from @target 

This obviously executes without error, but now uncomment the second insert line and the following error occurs:

Msg 2627, Level 14, State 1, Line 15 Violation of PRIMARY KEY constraint 'PK__#7DB3CB72__7EA7EFAB'. Cannot insert duplicate key in object 'dbo.@target'. 

I realise that the insert statement more than likely is effected against a snapshot of the @target table so (select max(id)+1 from @target) will always return a value of 1 – causing the violation error above…

Is there any way around this apart from resorting to a cursor?

Answer 1

Change your insert statement to the following:

insert into @target select (select max(id) from @target) + (ROW_NUMBER() OVER(ORDER BY s.id)), s.id from @source s

This should work for this specific case but I would be careful about generalizing it.