SQL is a standard language for accessing and manipulating databases.

Our SQL tutorial will teach you how to use SQL to access and manipulate data in MySQL, SQL Server, MS Access, Oracle, Sybase, DB2, and other database systems.

SQL is a Standard - BUT....

Although SQL is an ANSI (American National Standards Institute) standard, there are many different versions of the SQL language.

However, to be compliant with the ANSI standard, they all support at least the major commands (such as SELECT, UPDATE, DELETE, INSERT, WHERE) in a similar manner.

Note: Most of the SQL database programs also have their own proprietary extensions in addition to the SQL standard!
Using SQL in Your Web Site

To build a web site that shows some data from a database, you will need the following:

    * An RDBMS database program (i.e. MS Access, SQL Server, MySQL)
    * A server-side scripting language, like PHP or ASP
    * SQL
    * HTML / CSS

RDBMS

RDBMS stands for Relational Database Management System.

RDBMS is the basis for SQL, and for all modern database systems like MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access.

The data in RDBMS is stored in database objects called tables.

A table is a collections of related data entries and it consists of columns and rows.

SQL Syntax

Database Tables

A database most often contains one or more tables. Each table is identified by a name (e.g. "Customers" or "Orders"). Tables contain records (rows) with data.

Below is an example of a table called "Persons":

The table above contains three records (one for each person) and five columns (P_Id, LastName, FirstName, Address, and City).

SQL Statements

Most of the actions you need to perform on a database are done with SQL statements.

The following SQL statement will select all the records in the "Persons" table:
SELECT * FROM Persons

In this tutorial we will teach you all about the different SQL statements.
Keep in Mind That...

    * SQL is not case sensitive

Semicolon after SQL Statements?

Some database systems require a semicolon at the end of each SQL statement.

Semicolon is the standard way to separate each SQL statement in database systems that allow more than one SQL statement to be executed in the same call to the server.

We are using MS Access and SQL Server 2000 and we do not have to put a semicolon after each SQL statement, but some database programs force you to use it.
SQL DML and DDL

SQL can be divided into two parts: The Data Manipulation Language (DML) and the Data Definition Language (DDL).

The query and update commands form the DML part of SQL:

    * 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

The DDL part of SQL permits database tables to be created or deleted. It also define indexes (keys), specify links between tables, and impose constraints between tables. The most important DDL statements in SQL are:

    * 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

The SQL SELECT Statement

The SELECT statement is used to select data from a database.

The result is stored in a result table, called the result-set.
SQL SELECT Syntax
SELECT column_name(s)
FROM table_name

and
SELECT * FROM table_name

Note Note: SQL is not case sensitive. SELECT is the same as select.

SQL - Tutorial