As I mentioned in section , the purpose of a database is rapid data storage and retrieval. Today, most database systems are relational databases. While the term relational database has a mathematical foundation, practically it means that all data stored in the database is arranged in a uniform structure.
In figure , you see the database server with access to three
databases, test, demo, and finance.
You may ask, ``What are those black rectangles in the databases?'' Good question. Those are tables. Tables are the foundation of a relational database management system (RDBMS). As I mentioned earlier, databases store data. Those tables are where all the data is stored in a database. Each table has a name defined by the person who created it.
Let's look at a single table called friends in table .
Each friend is on a separate row. Each column contains the same type of information. This is the type of structure that makes relational databases successful. Relational databases allow you to select certain rows of data, certain columns of data, or certain cells. You could select the entire row for Mike, the entire column for City, or a specific cell like Denver. There are synonyms for the terms table, row, and column. Table is more properly referred to as a relation or class, row as record or tuple, and column as field or attribute.