SQL is a standard language for accessing databases.
Our SQL tutorial will teach you how to use SQL to access and manipulate data in:
MySQL, SQL Server, Access, Oracle, Sybase, DB2, and other database systems.
SQL Syntax
| SELECT Company, Country FROM Customers WHERE Country <> 'USA' |
SQL Result
| Company | Country |
|---|---|
| Island Trading | UK |
| Galería del gastrónomo | Spain |
| Laughing Bacchus Wine Cellars | Canada |
| Paris spécialités | France |
| Simons bistro | Denmark |
| Wolski Zajazd | Poland |
Introduction to SQL
SQL is a standard language for accessing and manipulating databases.
What is SQL?
- SQL stands for Structured Query Language
- SQL lets you access and manipulate databases
- SQL is an ANSI (American National Standards Institute) standard
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 (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 collection of related data entries and it consists of columns and rows.
SQL Syntax
Database Tables (Database Objects)
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":
| P_Id | LastName | FirstName | Address | City |
|---|---|---|---|---|
| 1 | Hansen | Ola | Timoteivn 10 | Sandnes |
| 2 | Svendson | Tove | Borgvn 23 | Sandnes |
| 3 | Pettersen | Kari | Storgt 20 | Stavanger |
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 defines indexes (keys), specifies links between tables, and imposes 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
