SQL transaction/ErrorHandling/TryandCatch - sql-server-2012

Question

Taking a SQL programming(2012 version) class and totally stuck, program wont work no matter how many times I try. The requirements (Questions) as well as what I have so far are below. Below the dashed line is another proc I wrote for error handling. Please help me finish this...please!
/*Create a Stored Procedure that accepts StockName, NewOpenPrice, NewClosePrice.
a. If the Stock Name does not EXIST a new record should be added into the dbo.Stocks table
b. If the Stock Name does EXIST, the OpenPrice an ClosePrice will be updated with the newly inserted Prices.
c. Insert and Update statements should be built using a transaction (Repeatable Read Isolation Level)
d. A Try Catch Statement should be used for the Update and Insert statements. If there is an error, the dbo.error_handler Stored Procedure should be called.
*/
CREATE PROCEDURE spc_Stocks
#Name varchar(25), #NewOpenPrice money, #NewClosePrice money
as
BEGIN
CREATE TABLE dbo.Stocks (
StockID int IDENTITY(1,1),
StockName varchar(50),
OpenPrice money,
ClosePrice money )
INSERT INTO dbo.Stocks
SELECT 'Walmart',21.58,22.98 UNION
SELECT 'Target',17.32,15.23 UNION
SELECT 'Taco Bell',4.58,12.98 UNION
SELECT 'Microsoft',7.15,8.15 UNION
SELECT 'Apple',10.79,9.89
Select StockName from stocks
where StockName = #Name
------Name does NOT exist
if (#Name = NULL)
Begin
Insert into dbo.Stocks (StockName)
Values (#Name)
END
----If name DOES exist
ELSE
BEGIN
Begin TRY
Begin SET TRANSACTION ISOLATION LEVEL REPEATABLE READ
UPDATE dbo.Stocks SET OpenPrice =#NewOpenPrice, ClosePrice= #NewClosePrice where StockName = #Name
Commit transaction
END TRY
BEGIN CATCH
?!?!?!?!?!?
*This is my ErrorHandler stored proc query
ALTER PROCEDURE dbo.error_handler
as
BEGIN
DECLARE #errnum INT,
#severity INT,
#errstate INT,
#proc NVARCHAR(126),
#line INT,
#message NVARCHAR(4000)
-- capture the error information that caused the CATCH block to be invoked
SELECT #errnum = ERROR_NUMBER(),
#severity = ERROR_SEVERITY(),
#errstate = ERROR_STATE(),
#proc = ERROR_PROCEDURE(),
#line = ERROR_LINE(),
#message = ERROR_MESSAGE()
end

Answer 1

Create PROCEDURE [dbo].[USP_Stocks]
(#Name varchar(25), #OpenPrice MONEY, #ClosePrice MONEY)
AS
BEGIN
-----Name does NOT exist
IF NOT EXISTS (SELECT StockName FROM [dbo].[Stocks]
WHERE StockName = #Name)
BEGIN
BEGIN TRY
SET TRANSACTION ISOLATION LEVEL REPEATABLE READ
BEGIN TRAN
INSERT INTO dbo.Stocks (StockName, OpenPrice, ClosePrice)
VALUES (#Name ,#OpenPrice, #ClosePrice)
COMMIT TRANSACTION
END TRY
BEGIN CATCH
EXEC dbo.error_handler
ROLLBACK
END CATCH
END
----If name DOES exist
ELSE
BEGIN
BEGIN TRY
SET TRANSACTION ISOLATION LEVEL REPEATABLE READ
BEGIN TRAN
UPDATE dbo.Stocks SET OpenPrice =#OpenPrice, ClosePrice= #ClosePrice
where StockName = #Name
Commit transaction
END TRY
BEGIN CATCH
ROLLBACK TRUANSACTION
EXEC dbo.error_handler
END CATCH
END
END