Question

I have a two column table with a primary key (int) and a unique value (nvarchar(255))

When I insert a value to this table, I can use Scope_identity() to return the primary key for the value I just inserted. However, if the value already exists, I have to perform an additional select to return the primary key for a follow up operation (inserting that primary key into a second table)

I’m thinking there must be a better way to do this – I considered using covered indexes but the table only has two columns, most of what I’ve read on covered indexes suggests they only help where the table is significantly larger than the index.

Is there any faster way to do this? Would a covered index be faster even if its the same size as the table?

Answer 1

Building an index won’t gain you anything since you have already created your value column as unique (which builds a index in the background). Effectively a full table scan is no different from an index scan in your scenario.

I assume you want to have a sort of insert-if-not-already-existsts behaviour. There is no way getting around a second select

if not exists (select ID from where name = @...)
   insert into ...
   select SCOPE_IDENTITY()
else 
   (select ID from where name = @...)

If the value happens to exist, the query will usually have been cached, so there should be no performance hit for the second ID select.