As there is an index that has the LastName and FirstName columns the optimiser has opted for an index seek operator using the IX_Person_LastName_FirstName_MiddleName index, and if I look into the Plan XML I can see that it’s using a trivial plan: StatementOptmLevel=”TRIVIAL”.
This basically means there’s one obvious way to return the query results so the optimiser has avoided the cost of going through full optimisation and has elected to use this plan straightaway.
So what happens if I create an identical copy of that particular index, in fact let’s create five indexes that are exactly the same:
There’s a Mass Effect 3 joke in my intro line. But read on for the answer and also check out Barney Lawrence’s comment for a bit more elucidation.