Question

Alright so a quick SQL question here(using sql-server-2008).

I have a mapping table names with the following columns

ID DisplayName

What I want to do is first
SELECT [ID] FROM [names] WHERE [DisplayName] = 'chuck';

BUT, if the name ‘chuck’ doesn’t exist in the database, I would like to create it, and return the auto incremented ID.

I was wondering if SQL had some built in way of doing this in an easy way, or if I have to go the long route?

long route being something like this

SELECT COUNT(ID) AS count, ID FROM names WHERE DisplayName='chuck'
IF(count > 0)
    SELECT ID as ReturnID;
ELSE
    BEGIN
    INSERT INTO names(DisplayName) values('chuck');
    SELECT scope_identity() as ReturnID;
    END

I didn’t test that last statement, but I assume the long way would be something like that. If there is no built in way, I’d appreciate it if someone could simply correct that statement(as I’m sure it isn’t completely correct).

Answer 1

You should take care about transactions as well:

set XACT_ABORT on
begin tran

declare @ID int

select @ID = ID from names with (holdlock, updlock) WHERE DisplayName='chuck'

if @@rowcount = 0
begin
  INSERT INTO names(DisplayName) values('chuck');
  set @ID = scope_identity();
end

select @ID as ReturnID;

commit tran

Note the usage of table hints – holdlock and updlock. They prevent another thread from executing exactly the same query and creating the row a second time. For more information look for isolation, synchronization, deadlocks, concurrent updates.