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. It can be shared by a wide variety of users with minimal redundancy and high data and program independence.

Today, 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)for defining, revoking, and altering data patterns.

(2) data Query Language (Language. DQL), which is used to query data.

(3) Data Manipulation language (manipulation Language. DML). Used to increase, delete and change data.

(4) Data Control Language (Language,DCL). Controls for access to data.

The data definition language contains the CREATE,DROP , and ALTER statements, and the data query language contains the 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 the actual software development project. Dealing with a variety of databases is a common occurrence. 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 openness, high performance and other characteristics, in the communication software products are widely used.

When we execute the Sybase database script, we will use a client software calledSybaseCentral, as seen in1 .

Figure 1 "SybaseCentral" client software interface

(2) Oracle database

Oracle Database is a relational database management system for Oracle Corporation. Now the market share in the database is the first. Its basic advantage is that it has distributed processing capability, and can handle large amount of data at the same time and maintain its performance stability.

It is because of this, in software products with a large user volume ( usually above millions ) . Oracle Database has a great advantage and a wide range of applications.

While executing the Oracle database script. We will use a "plsql Developer" Client software,2 see.

Figure 2 "plsql Developer" Client software interface

Other than that. As an open-source relational database management system. MySQL also has a certain application 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