sql server - trigger with a select condition -

i want create trigger doesn't perform insert if insert column 2 exists in table , value column 1 in table different value inserted column 1. i've done

create trigger tr1  on dbo.table  after insert, update   begin    declare @col1 varchar(20)   declare @col2 varchar(20)   if (    exists(    select column2 table    column2='@col2'         )    , @col1 <> select column1 table   column2='@col2'     )  begin   raiserror('error', 16, 1);   rollback  end end 

i'm not sure i've understood tryng easy way check existing values triggers use transaction tables.

• inserted update , insert
• deleted delete

1.

create table some_table(col1 int , col2 int) go 

2.

create trigger tr1 on dbo.some_table after insert, update begin      declare @cnt int       select          @cnt = count(*)      some_table t     inner join inserted on t.col1 = i.col1 , t.col2 = i.col2      if isnull(@cnt,0) > 1     begin       raiserror('error', 16, 1);        rollback     end end 

3.

insert some_table(col1, col2) values(1,2) go insert some_table(col1, col2) values(2,3) go --here trigger crash insert some_table(col1, col2) values(1,2) go 

i prefer unique index approach :)