Introduction to Databases

First, the database simple introduction

1, according to the development time sequence of the database, the following types of database system are mainly appeared:

Ø Web-based database

Ø Hierarchical Database

Ø relational database

Ø Object-oriented database

In the above 4 database system, the relational database is the most widely used. Object-oriented database is a new kind of database which is spawned by object-oriented language.

Some of the current database systems, such as SQL Server 2005, oracle10g, and so on, are beginning to add object-oriented features.

II. Common Basic SQL statements/syntax

ØSQL statement-based SQL is the standard language for manipulating and retrieving relational databases, and standard SQL statements can be used to manipulate and then relational databases.

Standard SQL statements are typically categorized into the following types:

Query statement: Mainly because the SELECT keyword is complete, the query statement is the most complex and most versatile statement in the SQL statement.

DML data munipulation Language, data manipulation language) statements, this set of DML statements will maintain a good consistency of information, the statement of the operation table, such as inserting, modifying, deleting, etc.;

DDL (data definition Language) statements, which manipulate the language of the data object, have Create, alter, and drop.

The DCL (Data Control Language) statement, which consists of the grant and REVOKE statements.

Transaction control Statements: Main commit, rollback, and savepoint three keywords complete

Ø Common query MySQL terminator is ";" End.

1, show all the database show databases;

2. Drop database dbName;

3. Create DATABASE [if not EXISTS] dbName; The brackets section is optional and determines that the data does not exist to create

4, switch, using the specified database use DbName;

Introduction to Databases