Help with CASE in Stored Procedure

hi guys! Help please..I'm new to sotred procedure. Currently, i have a stored procedure (see Below) but i can't figure out on how to solve the errors(see below). What im trying to do with my stored procedure is to take two(2) parameters, the string to be search(@.Search_Arg) and the search by(@.Search_by) Either by Login name or by firstname. Under my CASE statement, When the @.Search_by is equal to Username i want to select the user with User_login equals to @.Search_Arg and when the @.Search_by is equal to Firstname it will select all user with User_FirstName equals to @.Search_Arg...Any help please..Thanks in advance!

CREATE PROCEDURE sp_User_Search
@.Search_Arg varchar(50),
@.Search_By varchar(20)
AS
BEGIN

CASE @.Search_By
WHEN 'Username' THEN SELECT * FROM RCPS_UserAccount WHERE User_login = @.Search_Arg
WHEN 'Firstname' THEN SELECT * FROM RCPS_UserAccount WHERE User_FirstName = @.Search_Arg
END
END

Msg 156, Level 15, State 1, Procedure sp_User_Search, Line 7
Incorrect syntax near the keyword 'CASE'.
Msg 156, Level 15, State 1, Procedure sp_User_Search, Line 9
Incorrect syntax near the keyword 'WHEN'.
Msg 156, Level 15, State 1, Procedure sp_User_Search, Line 10
Incorrect syntax near the keyword 'END'.what you have there is a dynamic search condition. read this for various techniques:

http://www.sommarskog.se/dyn-search.html

in particular, this might suit you:

select col1, col2, col3 from RCPS_UserAccount
where
(User_login = @.user_login or @.user_login is null) and
(User_FirstName = @.user_firstname or @.user_firstname is null)|||Case can return only one value at a time
use of 'Select *' is not allowed in case statement. What you can do is :

CREATE PROCEDURE sp_User_Search
@.Search_Arg varchar(50),
@.Search_By varchar(20)
AS
BEGIN
SELECT * FROM RCPS_UserAccount
WHERE
CASE
When @.Search_By = 'Username' then
User_login
When @.Search_By = 'Firstname' then
User_FirstName
End
= @.Search_Arg
END
END

...but I think way suggested by jezemine is better than this one.sql