Filtering Data with WHERE
In the previous example, we selected all records from certain columns in the Products table. What if we only want to see products that sell for less than 25 When we want to filter data so that only records meeting certain criteria are retrieved, we can use a WHERE clause in our SQL statement, as shown below SELECT ProductName, UnitPrice, UnitsInStock FROM Products WHERE UnitPrice lt 25 The WHERE clause specifies that the UnitPrice should be less than 25, so that the above SQL statement will...
The User Interface
So you've learned how to design a database and how to update information in it using suitable SQL statements. We can't expect our users to open up an administrative database tool and manipulate the data directly like this, so our next step is to create some way for users to access information. This is the role of the user interface - to provide a means of communication between the user and the database. Through the user interface, users may interact with data and manipulate it in order to...
Paging
An age-old problem that faces web developers is that of presenting a single data source over multiple pages. Imagine you have 500 products that you need to display. Is it best to display a single page with all 500, or ten pages showing 50 products each Usually, the latter is best as it makes the finished product more approachable to the user, and because a huge quantity of data isn't being sent all at once. It's much more suited to the low bandwidth world of the Internet. Old style ASP lacked a...
Tkt Programming
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Info Cbj
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Info Wqn
3. If you look at the DataGrid control on the designer, you'll notice that it now shows exactly ten rows and that a set of page navigation buttons has appeared at the bottom. 4. Make these changes to btnSearch_Click in PriceCheck .aspx. vb Private Sub btnSearch_Click ByVal sender As System.Object, _ ByVal e As System.EventArgs Handles btnSearch.Click Dim connection As New SqlConnection Global.DbString connection.Open ' Retreive the items Dim sql As String _ SELECT productname, unitprice,...
Responding to Order Requests
Now that we can detect when a new file has been received, we should look at processing the order and sending the response by e-mail. Unlike the Web Service model, e-mail gives us maximum flexibility -we don't have to process an order as soon as we receive it and if we want, we can collect all orders received in a day and process them as a single batch. Imagine we receive an order for 100 widgets, but we only have 60. We ship 60, and create and e-mail an XML response document that informs the...
Bill Forgey
Bill writes I began my career in the early 1990's, originally an Electronic Engineering major and, soon after, the U.S. Navy. I soon found myself in a shut down engineering firm and was too stubborn to take anything less. My shipmate introduced me to VB 3.0 and Access 2.0 and, for the next few months, I found myself learning everything I could about VB. I began developing a phonebook program using VB and MS Access. I would program 12 to 14 hours a day, including all nighters or until my hands...
SMS Messaging
In this last section, we're going to use Salcentral to find a Web Service that we can call from our existing client application. Specifically, we're going to use their SMSMessaging Web Service. This Web Service can send a text message via SMS, the Short Message Service, to a handheld unit such as a compatible cell phone. Without a suitable Web Service, this is a particularly tricky proposition that can entail physically connecting a cell phone to your computer and controlling it through the...
ADOs Strengths and Weaknesses
ADO has stabilized to the point where it is very reliable and supported worldwide. You can easily apply the model to Windows and web applications. As it is supported by all Microsoft products, including Office, anyone with such a product on their system can run ADO applications. It can also be used for displaying or managing data in web pages. The following list provides a summary of ADO's main weaknesses It's only possible to manage one table or one set of records at a time There's no...
Info Glk
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Info Ula
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Info Lix
sql amp OrderID amp row orderid ' Do we need to bother If sql lt gt Then sql SELECT OrderID, ProductID, UnitPrice, Quantity, Discount amp FROM Order Details WHERE amp sql Dim detailsCommand As New SqlCommand sql, connection Dim detailsAdapter As New SqlDataAdapter detailsCommand detailsAdapter.Fill detailsTable ' Set the dataset property Me.DataSet newDataset ' Close the database connection.Close 3. Run the project and click Connect. You'll be able to use the plus buttons to show the Details...
Errata
We've made every effort to make sure that there are no errors in the text or in the code. However, no one is perfect and mistakes do occur. If you find an error in one of our books, like a spelling mistake or a faulty piece of code, we would be very grateful for feedback. By sending in errata, you may save another reader hours of frustration and, of course, you will be helping us provide even higher quality information. Simply e-mail the information to support wrox.com. Your information will be...
Flat File versus Relational Databases
Flat files are the most basic form of database - all of the information is stored in a single file. A flat file includes a field for every item of information that you need to store. While they are easy to create and can be useful in certain situations, flat files are not very efficient. They can be quite wasteful of storage space, containing a lot of duplicated information, especially in a complex system where multiple files hold connected information. This can make information harder to...