Chapters 3 and 4 reveal that creating a sound database structure is critical to maintaining data integrity. The stuff you're really interested in, however, is the data itself — not its structure. At any given time, you probably want to do one of four things with data: add it to tables, retrieve and display it, change it, or delete it from tables.
In principle, database manipulation is quite simple. Understanding how to add data to a table isn't difficult — you can add your data either one row at a time or in a batch. Changing, deleting, or retrieving one or more table rows is also easy in practice. The main challenge to database manipulation is selecting the rows that you want to change, delete, or retrieve. The data you want may reside in a database that contains a large volume of data you don't want. Fortunately, if you can specify what you want by using an SQL
SELECT statement, the computer does all the searching for you. I guess that means manipulating a database with SQL is a piece of cake. Adding, changing, deleting, and retrieving are all easy! (Hmmm. Perhaps that might be a slight exaggeration.) At least let's start off easy, with simple data retrieval.
The data-manipulation task that users perform most frequently is retrieving selected information from a database. You may want to retrieve the contents of one row out of thousands in a table. You may want to retrieve all rows that satisfy a condition or a combination of conditions. ...