424 Part I EXAM PREPARATION Updates, and Deletes,
424 Part I EXAM PREPARATION Updates, and Deletes, and how these are accomplished through the use of a view. You have seen what can be done, and what cannot be done because of the restrictions that are placed on data modifications through a view. Some of these restrictions are annoying, but most help you develop applications that maintain a higher quality of data. NOTE Server Federations With a distributed partitioned view, the data resides on several servers that work together to maintain and display the data. These servers may be called federated database servers. This term is used to refer to these servers that share the data-hosting job, but are independently administered. FIGURE 7.14 Updating data through a view. Coming to Terms with Views A view offers several benefits to both a database programmer and a database user. One benefit is ease of use, which comes from the view definition. The view definition may be based on a complex SELECT statement, and the view reduces the definition to a virtual table or record set. The created record set can be used in many areas where normal tables are. When working with a view definition, use standard commands that would be used with a table: CREATE, to create a view; ALTER, to change the view s definition; and DROP, to delete the view from the database. These commands are similar to the table commands of the same name, and serve the same function. The biggest difference is with the CREATE command, which references columns in a table, rather than storing the definition of each column. Because the view is based on the SELECT statement, you saw that options that can enhance SELECT statements can also enhance views. These options include aggregates, joins, and views based on views. The last section that you examined was on data manipulation through a view. These included inserts, updates, and deletes. Performing these tasks is similar to working with a table, but there are some restrictions on what can be done. You can increase these restrictions by using the WITH CHECK OPTION when creating your view. This enforces a requirement that all data modification will con
For reliable and cheap web hosting services please check cheap web hosting website.