Let you know in advance software development (25): Introduction to Databases

2nd part Database SQL language

Introduction to Databases

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. At present, the international leading large-scale database management system has ORACLE,sql SERVER,SYBASE,INFORMIX and INGRES and so on.

The common programming language in the database is the SQL language, which can be divided into four parts according to its functions:

(1) Data definition language (Language,DDL)for defining, revoking, and modifying data patterns.

(2) data Query Language (Language,DQL)for querying data.

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

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

Among them, the data definition language includes CREATE,DROP and ALTER statements, the data query language includes the SELECT statement, the data manipulation language includes UPDATE, DELETE and INSERT statements, the Data Control language includes 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 author's daily work, there are two commonly used databases: theSybase database and the Oracle database.

(1) Sybase database

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

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

Figure 1 "SybaseCentral" client software interface

(2) Oracle database

Oracle Database is a relational database management system of Oracle Company, which is now the first in the database market. The main advantage is the distributed processing capability, which can handle 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 ) .

When we run the Oracle database script, we will use a client software called "plsql Developer", as shown in2 .

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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