Task oriented processing And Queries

How do I want my information? A customer should not be required to remember An order number A product code An account code except for security purposes

Where is my…? A customer of Northwind wants to know Where is the order I placed last week? How much do I pay for Chai? How much more does Chai cost than Chang? What is the least expensive drink? What is the fanciest (most expensive) cheese?

How do I manage …? A line manager wants to know Are there any products that are out of stock? Are there any customers on the record that have never placed an order? Are there any employees who have never made a sale?

How do I save …? A managing director wants to know What is our best selling product? What is our highest earning product? Who is our highest earning employee? Who is the employee who sells the most units?

Formulating queries Ask the question the user would ask Avoid code-dependent queries – go for name-based or point and pick based queries. Once the query has been stated Consult the ERD Check the enquiry access path Try to fill the query using joins rather than separate queries.

Saving your queries in your database Stored Procedures Saving your queries in your database

Simple Stored Procedures Create the query and check it in the Query Analyser. Using the Enterprise Manager, Add a new stored procedure to your database. Name your Stored Procedure appropriately. Paste in your query, check syntax and click OK. Run your stored procedure from the query analyser using ‘EXEC <SP_NAME>.

Using variables Variables can be used in SQL Server using either the Query Analyser or Stored Procedures. All variables must begin with the symbol @ Variables must be given a data type: e.g. Declare @cost numeric(6,2); Declare @name varchar(20);

Using Variables Variables can be assigned values using Set: Set @cost = 0; Set @cost = @cost * 1.1; Or using Select: Declare @givenId numeric(7,0); Set @givenId = 1234567 Select @name = suppliername from Supplier where SupplierId = @givenId;

Parameters in Stored Procedures Parameters can be passed to stored procedures by reference. If the stored procedure is expected to return a significant value, then it should be explicitly marked as an output parameter. To use parameters: Define the formal parameters in the Stored Procedure. Define the actual parameters and give them values in the Query Analyser.

Exercise Write a stored procedure that will allow Joe to add an orderline to his database, decrementing the stock quantity in the stock table and returning a cost for that orderline. If there is not enough stock in the yard, a message should be displayed and the new orderline should be rejected.

Procedure specification Input: OrderNo, StockCode, QuantityRequired Output: The linecost To reject the request if the stock is not in the yard: Read the stock row Check the quantity If enough, Decrement stock Calculate line cost Update record Write new orderline Else Print error message

CREATE procedure sp_SELLSTOCK @DCKT numeric (5,0), @STKCD varchar(5), @QTYREQ numeric(4,0), @linecost numeric (7,2) OUTPUT as Begin Declare @QTY numeric(4,0) Set @linecost = 0 Select @qty = stock_level from stock where stock_code = @stkcd If @qty > @qtyreq Set @qty = @qty - @qtyreq print 'Quantity required = ' select @qtyreq Set @linecost = (select unit_price from stock where stock_code = @stkcd) print 'cost = ' select @linecost set @linecost = @linecost* @qtyreq print 'line cost = ' Update stock set stock_level = @qty where stock_code = @stkcd select @qty = quantity from order_line where stock_code = @stkcd and order_id =@dckt If @qty is null Insert into order_line values (@qtyreq, @stkcd, @dckt) else Update order_line set quantity = quantity + @qtyreq where stock_code = @stkcd and order_id = @dckt End print 'There are not enough items in stock'; end GO

To invoke sell stock and show results declare @cost numeric (7,2) set @cost = 0 exec sp_sellstock 5, e101, 2, @cost output; print 'cost =' select @cost; select * from jcustomer; select * from customerorder; select * from order_line; select * from stock; select * from Supplier;

Uses of stored Procedures This particular procedure can be used when Orders are being added. It only adds the orderline. All of the other information must be added outside this. Remember, most databases are accessed from an outside source such as JSP, ASP or Visual Basic.

Recording Joe’s Docket Populating multiple tables

Tables involved

How do you get the information in? Normally, this is done using a GUI, which populates a number of variables. We will cheat, by giving the variables values. Assume the stock being requested is: 10 of 3321 held as @QTY1, @STK1 14 of 5555 held as @QTY2, @STK2 2 of 1212 held as @QTY3, @STK3

We need to Generate a new docket number. Repeatedly ENTER the stock code and quantity being requested. Check to see if that stock is available. If so, decrement it from the stock and allocate it to the orderline. Write a new orderline. Put the system date and time onto the docket Write the docket.

Approach. 1. Have a rolling currentdocket, set on application launch. 2. Declare a function SellStock (DocketNo, StockCode, Quantity) This will take in the DocketNo, stock code and quantity and Check the stock table to see if the code exists and if there is enough stock. Write a new stock line. Return a cost value for the stock.

Generate a new docket number. This will be numerically one after the last docket. In the morning, when the system starts up, the last docket number used can be selected from the table: Declare @currentdocket int, docketdate datetime Select @currentdocket = top docketno from docket Before every new docket: Set @currentdocket = @currentdocket + 1

Repeatedly Write the docket. Repeatedly Select @Docketdate GETDATE() Insert into docket values docketno,,,docketdate Repeatedly Execute the SELLSTOCK procedure, varying the actual parameter values. Accumulate the linecosts from each sale

Not using interface – use variables variable_name := value SET @variable_name = value SELECT expression[, ...n] INTO variable_name[, ...n] FROM... SELECT {@variable_name = expression}[, ...n] FROM... FETCH cursor_name INTO variable_name[, ...n] FETCH [fetch option] FROM cursor_name INTO variable_name[, ...n]