SQL lessons with pictures and quizzes
This section defines in a simple way basic terms like tables, columns, rows, DBMS.
This section explains how to retrieve information in a database using SQL. It explains commands like SELECT, GROUP, JOIN.
This section explains how to insert and update information in a database using SQL.
This section explains how to create and modify database elements using SQL.
SQL practice and rehearsal tools:
Test your SQL skills by writing SQL queries against a real database.
This tool can help you rehearse SQL before an exam or a job interview.
What is SQL?
SQL is a programming language. SQL stands for Structured Query Language.
Its purpose is to send orders to a database, which is a source of information, to:
- retrieve information stored in this database.
- insert, update or delete information.
- modify the way this information is organised in this database.
- manage access rights to the database (who can access which information).
Example: your database contains information about a company’s customers, payments, employees… In order to retrieve the customer’s name and phone numbers in California, you would use a query written in SQL:
This query is sent to the database to retrieve this information and display it to you.
This is the type of information that the database would return:
History of SQL
In 1970, Edgar Codd, an IBM engineer, imagined a new type of database called “relational databases”. Relational databases offered a more flexible way of organizing data in databases. This work was an inspiration for the creators of the SQL language and of the first databases using SQL.
Engineers from IBM started to work on a project called System/R in 1974. Among them were Donald D. Chamberlin and Raymond F. Boyce based in sunny San Jose, California.
During this System/R project, they defined the SEQUEL language, which they renamed as SQL, because the name SEQUEL was already used by another company.
Although SQL was invented by IBM engineers, the first commercial database using SQL was sold by Oracle in 1979. IBM followed in 1981 with a product called SQL/DS, and in 1983 with a database called DB2. In 1989, Microsoft released commercially SQL Server. In 1994, Michael Widenius and David Axmark started working on the development of mySQL databases.
Latest Tricks (blog):
February 11, 2016 :
May 10, 2015 :
April 19, 2015 :
March 24, 2015 :
February 24, 2015 :
February 15, 2015 :