Let you know in advance software development (25): A brief introduction to the database

2nd part Database SQL language

Database Brief Introduction

A database is a generalized, comprehensive set of data that can be shared by a wide variety of users with minimal redundancy and high data and program independence. Now. The world-leading large database management system is ORACLE,sql SERVER,SYBASE,INFORMIX , and INGRES .

The programming languages used in the database are the SQL language, which can be divided into four parts according to their functions:

(1) Data definition language (Language,DDL). Used to define, REVOKE, and alter data patterns.

(2) data Query Language (Language. DQL). Used to query the data.

(3) Data Manipulation language (manipulation Language,DML)for adding, deleting, and changing data.

(4) Data Control Language (Language,DCL)for control of data access permissions.

The data definition language contains the CREATE,DROP , and ALTER statements. The data query language contains a SELECT statement. The data manipulation language contains UPDATE,DELETE , and INSERT statements, and the Data Control language contains the GRANT statement.

In the database, in addition to the above four kinds of SQL language, but also related to the concepts of tables, indexes, stored procedures and transactions, they are also indispensable in practical programming.

In actual software development projects, dealing with a variety of databases is a commonplace. In the daily work of the author. There are two types of databases that are used frequently: theSybase database and the Oracle database.

(1) Sybase database

Sybase launched the Sybase database product in 1987 year. This is a database based on the client /server architecture, because of its open, high performance and other characteristics, in the communication software products are widely used.

When we execute the Sybase database script, we use a client software calledSybaseCentral. 1 of what you see.

Figure 1 "SybaseCentral" client software interface

(2) Oracle database

Oracle Database is a relational database management system of Oracle Corporation, with the first share of the database market. Its basic strength is its distributed processing capability. It is possible to process large amounts of data at the same time and maintain the stability of its performance. Because of this,Oracle databases have great advantages and a wide range of applications in software products with a large user base ( typically above millions ) .

In the execution of Oracle database scripts, we will use a client software called "plsql Developer". 2 of what you see.

Figure 2 "plsql Developer" Client software interface

In addition, as an open-source relational database management system,MySQL also has some applications in small and medium-sized software products.

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Let you know in advance software development (25): A brief introduction to the database