MENU


SQL

SQL handles a relational database management system (RDMBS) in which a lot of data can be stored, modified and retrieved in an efficient and orderly manner. SQL is widely regarded as a fourth-generation language, which means that the commands are English-like and can be understood intuitively. We shall focus on MySQL, a popular open-sourced implementation of SQL acquired by Oracle.

MySQL commands can be issued to a MySQL server either through a direct front end such as PhpMyAdmin and MySQL Workbench, or through an external script such as a PHP script.

An SQL DBMS is typically organized into a collection of databases (also known as schemas). Each database contains a number of tables, views, stored procedures and functions. Each table or view, in turn, is made up of a number of relations (records). In this regard, the tables and views, where data is stored, are two-dimensional. Each row corresponds to a record or relation, and each column corresponds to a field.

We start by assuming that you already have access to a database and an account. We shall cover the more important concepts first. Advanced details will be discussed later.

The official documentation, which includes the various system variables and command-line options not covered here, can be found at:

http://dev.mysql.com/doc/refman/5.7/en/index.html

(This chapter reorganizes the official documentation and presents extra topics. Howerver, for the purpose of education, a few sections follow the official documentation closely. With due respect to the original writers, it is pointless to make changes to good writing.)

In this chapter, no meaningful example will be given until Query Functions. As you read Procedural Style Object Oriented Style Conventions of Functions Connection Functions, you may wish to refer to Query Functions and Object Oriented Style for two working examples. Study these two examples very carefully for they illustrate all the central concepts of SQL.