INSERT INTO [QOTD4] ([col1], [col2], [col3])
SELECT 1, 'w', 'something'
UNION ALL
SELECT 2, 'x', 'or other'
UNION ALL
SELECT 1, 'y', 'thing'
UNION ALL
SELECT 3, 'z', 'or what'

create table qotd4(col1 int not null, col2 char(1) not null, col3 varchar(20))
create unique index q04_index on qotd4(col1) with (ignore_dup_key=on)
go
begin tran
insert into qotd4(col1,col2,col3) values(1,'W','Some')
insert into qotd4(col1,col2,col3) values(2,'Y','Some')
insert into qotd4(col1,col2,col3) values(1,'X','Some')
insert into qotd4(col1,col2,col3) values(3,'Z','Some')
commit tran
go

select col2 from qotd4 order by col2
go
drop table qotd4

create table qotd4(col1 int not null, col2 char(1) not null, col3 varchar(20))
create unique index q04_index on qotd4(col1) with (ignore_dup_key=off)
go
begin tran
insert into qotd4(col1,col2,col3) values(1,'W','Some')
insert into qotd4(col1,col2,col3) values(2,'Y','Some')
insert into qotd4(col1,col2,col3) values(1,'X','Some')
insert into qotd4(col1,col2,col3) values(3,'Z','Some')
commit tran
go

select col2 from qotd4 order by col2
go
drop table qotd4

Msg 2601, Level 14, State 1, Line 4
Cannot insert duplicate key row in object 'dbo.qotd4' with unique index 'q04_index'.