The Language of SQL- P5: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. | 6 Chapter 1 Relational Databases and SQL Another distinction of Access compared to the other listed databases is that it is a desktop database. As such it has great flexibility. Not only can you use it to create a database that resides entirely in a single file on your PC but it also allows you to connect to more complex databases created with other tools such as Microsoft SQL Server. Relational Databases Let s look at the basics of relational databases and how they work. Basically a relational database is a collection of data stored in any number of tables. The term relational is used to indicate that the tables are related to each other. For example let s take the simple case of a database consisting of only two tables Customers and Orders. The Customers table contains one record for each customer who has ever ordered. The Orders table has one record for each order placed. Each table can contain any number of fields which are used to store the various attributes associated with each record. For example a Customer table might contain fields such as First Name and Last Name. At this point it s useful to visualize some tables and the data they contain. The common custom is to display a table as a grid of rows and columns. Each row represents a record in the table. Each column represents a field in the table. The top header row normally has the field names. The remaining rows show the actual data. In SQL terminology records and fields are actually referred to as rows and columns corresponding to the visual representation. So henceforth we ll use the terms rows and columns rather than records and fields to describe the design of tables in relational databases. Let s look at an example of the simplest possible relational database. In this database there are only two tables Customers and Orders. This is what these tables might look like Customers table CustomerlD FirstName LastName 1 William Smith 2 Natalie Lopez 3 Brenda Harper Primary and Foreign Keys 7 Orders table .
