Okay, for this sample

SELECT surname, firstname from TelephoneDirectory where PhoneNumber=@PhoneNumber)

Surname, firstname, address, phone number?

Firstname, surname, phonenumber, address?

Phonenumber, surname, firstname, address?

I suggest an index like this

CREATE NONCLUSTERED INDEX(PhoneNumber) INCLUDE(surname, firstname)

Something...

Hi

check for the grouping

you must add the right grouping likei

in Categroy Fields,

inner most must be grouped on both.

That should help.