612 Chapter14•ImplementingObjects Introduction SQL Server 2008 is a mature enterprise data platform, providing objects for storing, accessing, and modifying data. In this chapter you will discover how to create tables, indexes, stored procedures, functions, and triggers. Designing database objects and writing scripts for their creation is usually the role of database developers. However, database administrators must understand the concepts behind database objects and have the skills necessary to create and modify them. This chapter will provide you with these key skills. Database objects are divided into two broad categories: storage and programma- bility. Tables are units of data storage, structured by columns and rows. Each column in a table stores data of a specific data type. Many built-in data types are available for you to choose from, or you can create custom user-defined data types if necessary. Tables can store large amounts of data, which can take a long time to query. To maximize query performance, you can create fast lookup structures known as indexes. Indexes are created on frequently searched on columns and enable quick traversal when looking for particular values within a table, similar to the index you will find at the end of a printed book. You can associate constraints with table columns. Constraints define the rules to which data in a particular column or columns must adhere. For example, you can use a constraint to specify that values stored in the EMailAddress field are of a particular format. Unique constraints ensure that data for a particular column is unique across the table. For example, you may enforce that product names are always unique in the Products table. Constraints can also define relationships between tables, such as the necessity to have a Customer entity associated with every Order entity. These are known as foreign key constraints. Programmability objects allow you to define Transact-SQL statements that can be reused again and again. Views are based on Transact-SQL SELECT statements. They represent a way of viewing a data set and show data from one or more underlying tables. Views can be updated, allowing you to write data to the view and to update underlying tables. Stored procedures are compiled Transact-SQL statements that perform particular actions. Stored procedures can accept parameters and return values. Functions are similar to stored procedures, except that they always return a value and never update data. Triggers are actions defined on tables that will execute every time data in a table changes. Together these database objects compose a database system. Techniques and best practices for designing a database system are beyond the scope of this book. However you must understand the concepts behind database systems so that you can maintain them correctly and effectively. ImplementingObjects•Chapter14 613 Understanding DDL and DML Language Elements Transact-SQL is the language used to create objects and access data in SQL Server. Data Manipulation Language, (DML) is part of the Transact-SQL language that allows you to insert, modify, and delete data in SQL Server tables. The core state- ments that constitute DML are INSERT, UPDATE, DELETE, and MERGE. In this chapter you will only use these statements in a basic way, as they are outside the scope of this book and exam. Data Definition Language (DDL) is a subset of Transact-SQL that deals with creating database objects such as tables, constraints, and stored procedures. You will examine these statements in depth as they are mapped directly to the exam objectives. SQL Server 2008 Management Studio provides a rich user interface for creating these database objects. However, not all functionality is available within the user interface, and often you will use DDL scripts to create your database objects. The SQL Server 2008 Management Studio user interface simply allows you to create an underlying DDL statement using the appropriate GUI component. Figure 14.1 shows the user interface for creating a table. The DDL statement for creating the same table is shown in Example 14.1. Figure 14.1 SQL Server Management Studio User Interface 614 Chapter14•ImplementingObjects The key DDL statements are CREATE, ALTER, and DROP. The CREATE statement creates a SQL Server database object, like a table, view, or stored procedure. Example 14.1 creates a new table named Produce and a new view named Fruits. In this example we also use the INSERT DML statement to add three rows into our new table. Te s T Da y Ti p Remember that the user interface provided by SQL Server 2008 Management Studio allows you to visually design DDL statements. Any task that is available in SQL Server 2008 Management Studio can be completed using a DDL script, but not all options available within a DDL script are available within the user interface. Example 14.1 Using the CREATE DDL Statement to Create a New Table and View USE AdventureWorks; GO Use the CREATE DDL statement to create a new table named Produce CREATE TABLE Produce (ProductID int PRIMARY KEY, ProductName varchar(50), ProductType varchar(20)) Use the INSERT DML statement to add rows to the Produce table INSERT Produce VALUES (1, 'Tomato', 'Vegetable'), (2, 'Pear', 'Fruit'), (3, 'Kiwifruit', 'Fruit'); GO Use the CREATE DDL statement to create a new view named Fruit that shows us only produce of type 'Fruit' CREATE VIEW Fruit AS SELECT * FROM Produce WHERE ProductType = 'Fruit'; GO ImplementingObjects•Chapter14 615 The ALTER DDL statement changes an existing object and it can be used to add or remove columns from a table. You can also use this statement to change the definition of a view, stored procedure, trigger, or function. Example 14.2 adds a Price column to the Produce table we have created in Example 14.1. In this example we also redefine the view to include the new Price column. Do not confuse the ALTER statement, which changes an object definition, with the UPDATE statement, which changes data in a table. Use the SELECT statement to view the data in the Fruit View SELECT * FROM Fruit Results: ProductID ProductName ProductType 2 Pear Fruit 3 Kiwifruit Fruit Example 14.2 Using the ALTER DDL Statement to Add a New Column to a Table and Redefine a View Add a new column ALTER TABLE Produce ADD Price Money; GO Use the UPDATE statement to set prices UPDATE Produce SET Price = 2.50 WHERE ProductID = 1; UPDATE Produce SET Price = 3.95 WHERE ProductID = 2; UPDATE Produce SET Price = 4.25 WHERE ProductID = 3; GO Redefine the view ALTER VIEW Fruit AS SELECT ProductID, ProductName, Price FROM Produce WHERE ProductType = 'Fruit'; GO SELECT * FROM Fruit Results: 616 Chapter14•ImplementingObjects The DROP DDL statement removes an object from the database. If other objects depend on the object you are attempting to drop, this statement will not succeed and an error will be raised. Example 14.3 deletes data from the Produce table, and then removes both the Fruit view and the Produce table from the database. In this example, we also attempt to drop the Person.Contact table. This operation will fail, as other objects depend on Person.Contact. Do not confuse the DROP statement, which removes an object from the database, with the DELETE statement, which deletes data from a table. ProductID ProductName Price 2 Pear 3.95 3 Kiwifruit 4.25 Example 14.3 Using the DROP DDL Statement to Remove Tables and Views from a Database DELETE FROM Produce; SELECT * FROM Fruit; Results: ProductID ProductName Price (0 row(s) affected) DROP VIEW Fruit; GO DROP TABLE Produce; GO DROP TABLE Person.Contact; Results: Msg 3726, Level 16, State 1, Line 1 Could not drop object 'Person.Contact' because it is referenced by a FOREIGN KEY constraint. . procedures. You will examine these statements in depth as they are mapped directly to the exam objectives. SQL Server 2008 Management Studio provides a rich user interface for creating these database. using the appropriate GUI component. Figure 14.1 shows the user interface for creating a table. The DDL statement for creating the same table is shown in Example 14.1. Figure 14.1 SQL Server. function. Example 14.2 adds a Price column to the Produce table we have created in Example 14.1. In this example we also redefine the view to include the new Price column. Do not confuse the ALTER