SQL (STRUCTURED QUERY LANGUAGE)

INTRODUCTION: The Structured Query Language, known as SQL, is the main language used to create and manage database applications in computers. This means that almost development environment that deals with databases bases its structure on this language.

SQL can be pronounced Sequel or S. Q. L. we will consider the Sequel pronunciation. For this reason, the abbreviation will always be considered as a word, which would result in “A SQL statement” instead of “An SQL statement". Also, on this site, we will regularly write, “The SQL” instead of “The SQL language", as the L letter already represents the word Language.

SQL is a standard language and universally used. Like most other computer languages such as C, C++, Pascal, C#, or Java, you need a way to use it on your computer. This access is provided by a language engine that can receive your instructions and produce a result. In other words, you need a program that uses SQL as its means of communication. There are many of them in the market. They include Corel Paradox, Oracle, Microsoft Access, MySQL, Microsoft SQL Server, Sybase, etc. Some of these programs are easier to get, some are not.

SQL is the language used to access the data and structures within a relational database. PL/SQL (an Oracle specific SQL extension) allows basic program logic and control flow to be implemented around SQL statements. Most RDBMS vendors have a similar set of extensions or allow SQL statements to be embedded within a normal development package such as Visual Basic or C++.

When users have no idea of programming to works on the computer and perform work with the databases/tables, he uses a language to manipulate/extract the stored data from database/tables. The language designed for all such purposes is very simple and easy to use – that language is known as Structured Query Language (SQL). It is called query language because it is used to query (asks) some questions (queries) from tables and show results. It is called structures because of 2 reasons:

1.      It is made up (structured) of various commands and clauses like where, and, or etc.

2.      Although it is written in pure English rather than coding language but it has fixed syntaxes (structures). A user has to follow these structures or syntaxes.

It enables the user to create and operate on relational database (RDB). The set of information which a user wants to store can be stored in the form of rows and columns. The SQL allow the user to deal with such set of commands like CREATE, RETRIEVE, transfer of information etc.

The original version of SQL was signed by IBM and that version was known as SEQUEL. SQL is used for following purposes.

¨      To create data tables.

¨      To insert values into tables.

¨      To define relationship between two or more tables.

¨      To extract data from related tables.