MS SQL Check for duplicate in two fields - sql-server

Question

I am trying create a trigger that will check if the Author already exist in a table based on a combination of their first and last name. From what Ive been reading this trigger should work, but when I try to insert any new author into the table it gives the "Author exists in table already!" error even though I am inserting an author that does not exist in the table.
Here is the trigger
USE [WebsiteDB]
GO
CREATE TRIGGER [dbo].[tr_AuthorExists] ON [dbo].[Authors]
AFTER INSERT
AS
if exists ( select * from Authors
inner join inserted i on i.author_fname=Authors.author_fname AND i.author_lname=Authors.author_lname)
begin
rollback
RAISERROR ('Author exists in table already!', 16, 1);
End
Here is the table
CREATE TABLE [dbo].[Authors](
[author_id] [int] IDENTITY(1,1) NOT NULL,
[author_fname] [nvarchar](50) NOT NULL,
[author_lname] [nvarchar](50) NOT NULL,
[author_middle] [nvarchar](50) NULL,
CONSTRAINT [PK_Authors] PRIMARY KEY CLUSTERED
(
[author_id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
Any assistance would be appreciated!

Answer 1

You will need to do this as an INSTEAD of trigger. This also means you need to actually perform the insert inside the trigger. Something along these lines.
CREATE TRIGGER [dbo].[tr_AuthorExists] ON [dbo].[Authors]
instead of insert
AS
set nocount on;
if exists
(
select * from Authors a
inner join inserted i on i.author_fname = a.author_fname AND i.author_lname = a.author_lname
)
begin
rollback
RAISERROR ('Author exists in table already!', 16, 1);
End
else
insert Authors
select i.author_fname
, i.author_lname
, i.author_middle
from inserted i