Got it! Use @P_Condition varchar(30) as parameter, because @P_Condition varchar represents only one character.
Have a nice day.
ALTER PROCEDURE [dbo].[ADMN_INSMAIN_FETCH]
@P_Condition varchar(30) ,@P_Mode varchar,@P_Entryby int
,@P_MAIN_INST_ID int,@P_MAIN_INST_MAME varchar
AS
BEGIN
if (@P_Condition='getmaster')
begin
select ADMN_INSTN_MASTER.*,ADMN_INSTN_MAIN.MAIN_INST_MAME from ADMN_INSTN_MASTER
inner join ADMN_INSTN_MAIN on ADMN_INSTN_MAIN.MAIN_INST_ID=ADMN_INSTN_MASTER.MAIN_INST_ID ;
end
END