In That Code Update Statement Not Working And If I Delete Means The Entire Row Is Deleted I Want Deleted Transaction For That I Have To Create Any Separate Table?If It Means Please Do The Needful.

create table tbl_cyl_gas_master
(
serial_no int primary key identity(1,1),
gas_name varchar(50),
tran_stat varchar(50))

create procedure gas
(
@action varchar(20),
@serial_no int,
@gas_name varchar(50),
@tran_stat varchar(50)
)
as
BEGIN
SELECT @tran_stat = tran_stat, @serial_no = serial_no, @gas_name = gas_name FROM tbl_Cyl_gas_master WHERE serial_no=@serial_no
IF(@tran_stat ='')
SET @tran_stat = CASE when @action='ADD' then 'FR' END
declare       @tran_stat_exists    varchar(2)
declare @serialno_exists varchar(10)
declare @gas_name_exists varchar(50)
                     select  @gas_name_exists=gas_name from   tbl_cyl_gas_master where gas_name like @gas_name
IF(@action ='add')
BEGIN
       if @gas_name_exists = @gas_name
       begin
              Raiserror('Gas Name already added',16,1)
       end
       else
       begin
              INSERT INTO tbl_Cyl_gas_master(gas_name,tran_stat) VALUES (@gas_name,@tran_stat)
       end   
END
ELSE IF @action='update'
BEGIN
IF (@tran_stat = 'FR')
UPDATE tbl_Cyl_gas_master set gas_name=@gas_name,@tran_stat = @tran_stat WHERE serial_no=@serial_no
ELSE
RAISERROR ('Transaction not is fresh',16,1);
END
ELSE IF @action='authorise'
BEGIN
IF (@tran_stat = 'FR')
UPDATE tbl_Cyl_gas_master SET tran_stat='AU' WHERE serial_no=@serial_no
ELSE
begin
RAISERROR ('Transaction already Authorised',16,1)
end
END
ELSE
      
              DELETE from tbl_Cyl_gas_master where serial_no=@serial_no
    
END