Merge into desttable as target
using 
(
select col1, col2,col3,col4,col5 from sourcetable
except
select col1, col2,col3,col4,col5 from desttable

) as source
on target.col1=source.col1 -- (use primary key )
when matched then 
update set target.col1=source.col1,
.......

when not matched bye target then insert 
(col1,col2,col3,col4,col5) values (source.col1,.....)

CREATE TABLE #author2 (cola  VARCHAR(50),colb  VARCHAR(50), action_flag VARCHAR(10)  ) 

CREATE TABLE dbo.author1 
  ( cola VARCHAR(50),  colb VARCHAR(50)  ) 

CREATE TABLE dbo.authors 
  (  au_fname VARCHAR(100), au_lname VARCHAR(100) 
  ) 

MERGE INTO authors AS target 
using (SELECT cola, 
              colb 
       FROM   author1 
       EXCEPT 
       SELECT au_fname, 
              au_lname 
       FROM   authors) AS source 
ON target.au_fname = source.cola 
WHEN matched THEN 
  UPDATE SET target.au_lname = source.colb 
WHEN NOT matched BY target THEN 
  INSERT (au_fname, 
          au_lname) 
  VALUES(source.cola, 
         source.colb) 
WHEN NOT matched BY source THEN 
  DELETE 
output ( CASE 
           WHEN $action = 'DELETE' THEN deleted.au_fname 
           ELSE inserted.au_fname 
         END )au_fname, 
       ( CASE 
           WHEN $action = 'DELETE' THEN deleted.au_lname 
           ELSE inserted.au_lname 
         END )colb, 
       $action 
INTO #author2;