MONDE-HISTOIRE-CULTURE GÉNÉRALE
Vous souhaitez réagir à ce message ? Créez un compte en quelques clics ou connectez-vous pour continuer.
MONDE-HISTOIRE-CULTURE GÉNÉRALE

Vues Du Monde : ce Forum MONDE-HISTOIRE-CULTURE GÉNÉRALE est lieu d'échange, d'apprentissage et d'ouverture sur le monde.IL EXISTE MILLE MANIÈRES DE MENTIR, MAIS UNE SEULE DE DIRE LA VÉRITÉ.
 
AccueilAccueil  PortailPortail  GalerieGalerie  RechercherRechercher  Dernières imagesDernières images  S'enregistrerS'enregistrer  Connexion  
Derniers sujets
Marque-page social
Marque-page social reddit      

Conservez et partagez l'adresse de MONDE-HISTOIRE-CULTURE GÉNÉRALE sur votre site de social bookmarking
QUOI DE NEUF SUR NOTRE PLANETE
LA FRANCE NON RECONNAISSANTE
Ephémerides

 

 SQL Basics :introduction

Aller en bas 
AuteurMessage
mihou
Rang: Administrateur
mihou


Nombre de messages : 8092
Localisation : Washington D.C.
Date d'inscription : 28/05/2005

SQL Basics :introduction Empty
03022006
MessageSQL Basics :introduction

http://www.commentcamarche.net/sql/

Introduction to SQL


SQL is a standard computer language for accessing and manipulating databases.
What is SQL?
SQL stands for Structured Query Language
SQL allows you to access a database
SQL is an ANSI standard computer language
SQL can execute queries against a database
SQL can retrieve data from a database
SQL can insert new records in a database
SQL can delete records from a database
SQL can update records in a database
SQL is easy to learn
SQL is a Standard - BUT....

SQL is an ANSI (American National Standards Institute) standard computer language for accessing and manipulating database systems. SQL statements are used to retrieve and update data in a database. SQL works with database programs like MS Access, DB2, Informix, MS SQL Server, Oracle, Sybase, etc.

Unfortunately, there are many different versions of the SQL language, but to be in compliance with the ANSI standard, they must support the same major keywords in a similar manner (such as SELECT, UPDATE, DELETE, INSERT, WHERE, and others).

Note: Most of the SQL database programs also have their own proprietary extensions in addition to the SQL standard!
SQL 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":
LastName FirstName Address City
Hansen Ola Timoteivn 10 Sandnes
Svendson Tove Borgvn 23 Sandnes
Pettersen Kari Storgt 20 Stavanger

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

With SQL, we can query a database and have a result set returned.

A query like this:

SELECT LastName FROM Persons

Gives a result set like this:
LastName
Hansen
Svendson
Pettersen

Note: Some database systems require a semicolon at the end of the SQL statement. We don't use the semicolon in our tutorials.
SQL Data Manipulation Language (DML)

SQL (Structured Query Language) is a syntax for executing queries. But the SQL language also includes a syntax to update, insert, and delete records.

These query and update commands together form the Data Manipulation Language (DML) part of SQL:
SELECT - extracts data from a database table
UPDATE - updates data in a database table
DELETE - deletes data from a database table
INSERT INTO - inserts new data into a database table
SQL Data Definition Language (DDL)

The Data Definition Language (DDL) part of SQL permits database tables to be created or deleted. We can also define indexes (keys), specify links between tables, and impose constraints between database tables.

The most important DDL statements in SQL are:
CREATE TABLE - creates a new database table
ALTER TABLE - alters (changes) a database table
DROP TABLE - deletes a database table
CREATE INDEX - creates an index (search key)
DROP INDEX - deletes an index



Type de donnée Syntaxe Description
Type alphanumérique CHAR(n) Chaîne de caractères de longueur fixe n (n<16383)
Type alphanumérique VARCHAR(n) Chaîne de caractères de n caractères maximum (n<16383)
Type numérique NUMBER(n,[d]) Nombre de n chiffres [optionnellement d après la virgule]
Type numérique SMALLINT Entier signé de 16 bits (-32768 à 32757)
Type numérique INTEGER Entier signé de 32 bits (-2E31 à 2E31-1)
Type numérique FLOAT Nombre à virgule flottante
Type horaire DATE Date sous la forme 16/07/99
Type horaire TIME Heure sous la forme 12:54:24.85
Type horaire TIMESTAMP Date et Heure
Revenir en haut Aller en bas
https://vuesdumonde.forumactif.com/
Partager cet article sur : reddit

SQL Basics :introduction :: Commentaires

Aucun commentaire.
 

SQL Basics :introduction

Revenir en haut 

Page 1 sur 1

 Sujets similaires

-
» SQL Basics :INSERT INTO
» SQL Basics :DELETE FROM
» SQL Basics :WHERE clause
» SQL Basics :CREATE
» SQL Basics :TRIGGERS

Permission de ce forum:Vous ne pouvez pas répondre aux sujets dans ce forum
MONDE-HISTOIRE-CULTURE GÉNÉRALE :: SCIENCES :: INFORMATIQUE-INTERNET/COMPUTER SCIENCES-
Sauter vers: