The Basics of Databases in Java

Painting QR Code in Java The Basics of Databases

Although such a rigid structure might seem to make flat-file databases harder to use, it does make flat-file databases easier to search and sort information Unlike free-form databases that may contain anything, every record in a flatfile database contains the exact same type of information, such as a name, address, and phone number This makes it possible to search and sort data If you want to find the telephone number of Robert Jones, you could tell the flat-file database to show you all the records that contain a first name beginning with the letter R If you want to sort your entire database alphabetically by last name, you can do that, too A flat-file database gets its name because it can work only with one file at a time This makes a flat-file database easy to manage but also limits its usefulness If you have a flat-file database containing names and addresses and a second flat-file database containing names and telephone numbers, you might have identical names stored in the two separate files Change the name in one flat-file database and you need to change that same name in the second flat-file database

For storing simple, structured information, such as names, addresses, and phone numbers (similar to a Rolodex file), flat-file databases are adequate However, if you need to store large amounts of data, you re better off using a relational database, which is what the majority of database programs offer Like a flat-file database, you can t store anything in a relational database until you define the number and size of your fields to specify exactly what type of information (such as names, phone numbers, and e-mail addresses) that you want to save Unlike flat-file databases, relational databases can further organize data into groups, or tables Whereas a free-form database stores everything in a file and a flat-file database stores everything in file, but organizes it into fields; a relational database stores everything in a file that s divided into tables, which are further divided into fields, as shown in Figure 1-3 Think of database tables as miniature flat-file databases that can connect with each other Just as storing a name in separate First Name and Last Name fields gives you more flexibility in manipulating your data, grouping data in separate tables also give you more flexibility in manipulating and sharing information

Customers Bo Katz 948 Main Street Baltimore, MD 01478 Prospects Bogg Smith 153 Main Street Detroit, MI 48154

Tables Temp workers Ann Johnson 43 Parkway Boston, MA 01245 Contractors Ian Slater 934 Black Drive San Francisco, CA 94781

Suppose you have a list of employees that includes names, addresses, and telephone numbers Now you may want to organize employees according to the department where they work With a flat-file database, you d have to create a separate file and store duplicate names in these separate databases, as shown in Figure 1-4 Every time you add a new employee, you d have to update both the employee database and the specific department database that defines where he works If an employee leaves, you d have to delete his name from two separate databases as well With identical information scattered between two or more databases, keeping information updated and accurate is difficult Relational databases solve this problem by dividing data into tables with a table grouping the minimum amount of data possible So, one table might contain names and employee ID whereas a second table might contain only employee names and department names, as shown in Figure 1-5

Name Bill Adams Sally Tarkin Johnny Brown Doug Hall Yolanda Lee Sam Collins Randy May Al Neander Kal Baker Employee ID 4Y78 8U90 4T33 4A24 9Z49 1Q55 2E03 4M79 2B27 Name Bill Adams Sally Tarkin Johnny Brown Doug Hall Yolanda Lee Sam Collins Randy May Al Neander Kal Baker