What is SQL?

SQL is a standard language for accessing and manipulating databases.

• SQL stands for Structured Query Language

• SQL lets you access and manipulate databases

• SQL became a standard of the American National Standards Institute (ANSI) in 1986, and of the International Organization for Standardization (ISO) in 1987

What Can SQL do?

• SQL can execute queries against a database

• SQL can retrieve data from a database

• SQL can insert records in a database

• SQL can update records in a database

• SQL can delete records from a database

• SQL can create new databases

• SQL can create new tables in a database

• SQL can create stored procedures in a database

• SQL can create views in a database

• SQL can set permissions on tables, procedures, and views

SQL is a Standard - BUT....

Although SQL is an ANSI/ISO standard, there are 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 data from a database, you will need:

• An RDBMS database program (i.e. MS Access, SQL Server, MySQL)

• To use a server-side scripting language, like PHP or ASP

• To use SQL to get the data you want

• To use HTML / CSS to style the page

RDBMS

RDBMS stands for Relational Database Management System.

RDBMS is the basis for SQL, and for all modern database systems such as 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 collection of related data entries and it consists of columns and rows.

Look at the "Customers" table:

Example

SELECT * FROM Customers;

The columns in the "Customers" table consist of CustomerID, CustomerName, ContactName, Address, City, PostalCode and Country. A column is a vertical entity in a table.

Some of The Most Important SQL Commands

• 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