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.
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
Begin
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 = '
select @linecost
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
else
Begin
print 'There are not enough items in stock';
end
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
Staff
Stock
Staff name
Staff no
Staff role
Stock Code
Stock Description
Unit Price
*Supplier Id
UnitCostPrice
Stock level
Reorder level
Docket
DocketNo
Order Date
*Customer Id
DocketPaidSig
DocketRcvdSig
*Staff no
Order Line
*DocketNo
*Stock Code
QuantityRequired
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.
– 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]