[sql-server] Creating stored procedure with declare and set variables

I am creating one stored procedure where only value has to pass and I have to retrieve multiple values from multiple tables. I tried to do like this but its showing errors like

Incorrect Syntax near Begin

and

Must declare the scalar variable @OrderID

Declare @OrderItemID AS INT
DECLARE @AppointmentID AS INT
DECLARE @PurchaseOrderID AS INT
DECLARE @PurchaseOrderItemID AS INT
DECLARE @SalesOrderID AS INT
DECLARE @SalesOrderItemID AS INT

SET @OrderItemID = (SELECT OrderItemID FROM [OrderItem] WHERE OrderID = @OrderID)

SET @AppointmentID = (SELECT  AppoinmentID FROM [Appointment] WHERE OrderID = @OrderID)

SET @PurchaseOrderID = (SELECT  PurchaseOrderID FROM [PurchaseOrder] WHERE OrderID = @OrderID)

You should try this syntax - assuming you want to have @OrderID as a parameter for your stored procedure:

CREATE PROCEDURE dbo.YourStoredProcNameHere
   @OrderID INT
AS
BEGIN
 DECLARE @OrderItemID AS INT
 DECLARE @AppointmentID AS INT
 DECLARE @PurchaseOrderID AS INT
 DECLARE @PurchaseOrderItemID AS INT
 DECLARE @SalesOrderID AS INT
 DECLARE @SalesOrderItemID AS INT

 SELECT @OrderItemID = OrderItemID 
 FROM [OrderItem] 
 WHERE OrderID = @OrderID

 SELECT @AppointmentID = AppoinmentID 
 FROM [Appointment] 
 WHERE OrderID = @OrderID

 SELECT @PurchaseOrderID = PurchaseOrderID 
 FROM [PurchaseOrder] 
 WHERE OrderID = @OrderID

END

OF course, that only works if you're returning exactly one value (not multiple values!)

I assume you want to pass the Order ID in. So:

CREATE PROCEDURE [dbo].[Procedure_Name]
(
    @OrderID INT
) AS
BEGIN
    Declare @OrderItemID AS INT
    DECLARE @AppointmentID AS INT
    DECLARE @PurchaseOrderID AS INT
    DECLARE @PurchaseOrderItemID AS INT
    DECLARE @SalesOrderID AS INT
    DECLARE @SalesOrderItemID AS INT

    SET @OrderItemID = (SELECT OrderItemID FROM [OrderItem] WHERE OrderID = @OrderID)
    SET @AppointmentID = (SELECT AppoinmentID FROM [Appointment] WHERE OrderID = @OrderID)
    SET @PurchaseOrderID = (SELECT PurchaseOrderID FROM [PurchaseOrder] WHERE OrderID = @OrderID)
END