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The Language of SQL- P38

The Language of SQL- P38: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. | Looking Ahead 171 Looking Ahead In this chapter we ve seen that the use of parameters can add a great deal of flexibility to the process of retrieving data. For example parameters allow you to generalize SQL statements so that values for selection criteria can be specified at the time the statement is executed. You ve also learned the basics of how to create and modify stored procedures. Finally we explained some of the differences between stored procedures and user-defined functions. Although the examples in the present chapter were focused on data retrieval stored procedures and functions are also quite useful in applying data updates. Our next chapter Modifying Data will take us completely out of the realm of data retrieval and move us squarely into issues surrounding the need to update data. The business of maintaining data doesn t present the same analytic possibilities as data retrieval but it is a necessary task for any enterprise. Fortunately most of the techniques you ve learned with the SELECT statement apply equally to the modification processes to be discussed in the next chapter. This page intentionally left blank CHAPTER 17 Modifying Data Keywords Introduced INSERT INTO VALUES DELETE TRUNCATE TABLE UPDATE Having exhausted our discussion of retrieving data from databases we will now move on to the topic of how to modify data. There are three basic scenarios as to how data can be modified Inserting new rows into a table Deleting rows from a table Updating existing data in specific rows and columns in a table As you may surmise inserting and deleting rows is relatively straightforward. Updating existing data however is a more complex endeavor. We ll begin with the insert and delete functions and then conclude with updates. Modification Strategies The mechanics of modifying data are fairly straightforward. However the nature of the process means that this is an area fraught with danger. Being human mistakes can be made. With a single command you can .