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The Language of SQL- P41

The Language of SQL- P41:Research has shown that, being pressed for time, most readers tend to skip the introduction of any book they happen to read and then proceed immediately to the first real chapter. With that fact firmly in mind, we will only cover relatively unimportant material in the introduction, such as an explanation of what you will and will not learn by reading this book. | 186 Chapter 18 Maintaining Tables The CREATE VIEW and CREATE PROCEDURE statements are DDL because they only allow you to manipulate the database itself. They have nothing to do with the data in databases. In this chapter we re going to give a brief overview of a few additional DDL statements which can be utilized to create and modify tables and indexes. Each database has a different way of organizing its objects and therefore has different available DDL statements. For example MySQL has 11 different CREATE statements for these types of objects Databases Events Functions Indexes Logfile Groups Procedures Servers Tables TableSpaces Triggers and Views. Oracle has over 30 different CREATE commands for the object types in its database. Microsoft SQL Server has over 40 different CREATE commands for its object types. In truth most modifications to database objects such as views and tables can be accomplished through the visual GUI graphical user interface which each software vendor provides to administer their software. It is often not necessary to learn any DDL at all since it can usually be handled with the software GUI. However it s useful at least to be aware of the existence of a few key statements to manipulate data objects. We ve already seen some statements that allow us to modify views and stored procedures. In this chapter we ll show you some of the possibilities for modifying tables and indexes via DDL. Table Attributes In Chapter 1 we briefly discussed a few attributes of database tables such as primary keys foreign keys and datatypes. In Chapter 2 we extended that discussion to talk about auto-increment columns. As mentioned SQL DDL provides CREATE statements for many types of database objects. In Chapter 13 we talked about the CREATE PROCEDURE and CREATE VIEW statements that handle stored procedures and views. We re now going to bring our attention back to tables. Tables are perhaps the primary and most essential object type in a database. Without tables .