I want to use CASE statement to update some records in sql server 2005

Question

UPDATE dbo.TestStudents  

SET LASTNAME = 

( CASE  

WHEN (LASTNAME = 'AAA') THEN 'BBB' 

WHEN (LASTNAME = 'CCC') THEN 'DDD' 

WHEN (LASTNAME = 'EEE') THEN 'FFF' 

ELSE  (LASTNAME)

END )

The statement work for the purpose but the else condition scan through every record in the table. Is there any way I can leave the unaffected rows as they are?

Answer 1

Try adding a WHERE clause like this:

UPDATE dbo.TestStudents  

SET     LASTNAME =  CASE  

                        WHEN LASTNAME = 'AAA' THEN 'BBB' 

                        WHEN LASTNAME = 'CCC' THEN 'DDD' 

                        WHEN LASTNAME = 'EEE' THEN 'FFF' 

                        ELSE LASTNAME

                    END 

WHERE   LASTNAME IN ('AAA', 'CCC', 'EEE')