sql server - Update trigger that affects only modified columns -

i trying create trigger update columns if value has been changed. i've read done comparing inserted , deleted tables. below how i'm trying comparison.

is there other way? think select queries , if statements can nested in ways, can't figure out how.

create trigger [dbo].[tr_persoane_update]    on [dbo].[persoane]    after update begin     set nocount on;      declare @dfirstname varchar(30),              @ifirstname varchar(30),              @dlastname varchar(30),             @ilastname varchar(30)      select  @dfirstname=d.firstname, @dlastname=d.lastname     deleted d     select  @ifirstname=i.firstname, @ilastname=i.lastname     inserted      if @dfirstname <> @ifirstname         begin             update firstname             set  firstname = @ifirstname             firstname = @dfirstname         end     if @dlastname <> @ilastname          begin             update lastname             set  lastname = @ilastname             lastname = @dlastname         end   end 

i tried approach, fail use case statement properly.

alter trigger [dbo].[tr_persons_update]    on [dbo].[persons]    after update begin     set nocount on;     select  d.firstname, d.lastname, d.id_title, i.firstname, i.lastname, i.id_title,             case when d.firstname <> i.firstname                                             begin                             update persons                             set  firstname = i.firstname                             firstname = d.firstname                             print 'firstname modified'                         end             /*end                                    case*/ when d.lastname <> i.lastname                                             begin                             update persons                             set  lastname = i.lastname                             lastname = d.lastname                             print 'lastname modified'                         end              /*end                                    case*/ when d.id_title <>   i.id_title                                             begin                             update persons                             set id_title=i.id_title                             id_title=d.id_title                         end             end     deleted d         inner join inserted on d.id_person=i.id_person end 

here example first name:

update fn     set firstname = id.newfname     firstname fn join          (select i.firstname newfname, d.firstname oldfname           inserted join                deleted d                on i.personid = d.personid           i.firstname <> d.firstname          ) id          on fn.firstname = id.oldname; 

you shouldn't assume inserted , deleted contain 1 value. requires id matches 2 view (inserted , deleted views , not tables).