What is SQL?

SQL stands for Structured Query Language, SQL is a standard language for accessing databases, SQL has been an international standard (ISO) since 1987

SQL Statements

To access a database, you use SQL statements.

The following SQL statement selects all records in a database table called "Customers":

Example

SELECT * FROM Customers;

Database Tables

A database most often contains one or more tables.

Each table is identified by a name like "Customers" or "Orders".

Below is a selection from a "Customers" table:

ID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

The table above contains five records (one for each customer) and seven columns:

1. CustomerID (ID)
2. CustomerName
3. ContactName
4. Address
5. City
6. PostalCode
7. Country

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The Most Important SQL Statements:

• SELECT - extracts data from a database
• UPDATE - updates data in a database
• DELETE - deletes data from a database
• INSERT INTO - inserts new data into a database
• CREATE DATABASE - creates a new database
• ALTER DATABASE - modifies a database
• CREATE TABLE - creates a new table
• ALTER TABLE - modifies a table
• DROP TABLE - deletes a table
• CREATE INDEX - creates an index (search key)
• DROP INDEX - deletes an index

SQL keywords are NOT case sensitive: select is the same as SELECT

Full SQL Tutorial

This has been a short introduction to SQL.

For a full SQL tutorial go to W3Schools SQL Tutorial.