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  #21  
Старый 26.12.2009, 03:55
Marley Marley вне форума
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По умолчанию Relational Database Terminology



Terminology Used in a Relational Database

A relational database can contain one or many tables. A table is the basic storage structure of an RDBMS. A table holds all the data necessary about something in the real world, such as employees, invoices, or customers.

The slide shows the contents of the EMPLOYEES table or relation. The numbers indicate the following:

1. A single row (or tuple) representing all data required for a particular employee. Each row in a table should be identified by a primary key, which permits no duplicate rows. The order of rows is insignificant; specify the row order when the data is retrieved.

2. A column or attribute containing the employee number. The employee number identifies a unique employee in the EMPLOYEES table. In this example, the employee number column is designated as the primary key. A primary key must contain a value, and the value must be unique.

3. A column that is not a key value. A column represents one kind of data in a table; in this example, the data is the salaries of all the employees. Column order is insignificant when storing data; specify the column order when the data is retrieved.

4. A column containing the department number, which is also a foreign key. A foreign key is a column that defines how tables relate to each other. A foreign key refers to a primary key or a unique key in the same table or in another table. In the example, DEPARTMENT_ID uniquely identifies a department in the DEPARTMENTS table.

5. A field can be found at the intersection of a row and a column. There can be only one value in it.

6. A field may have no value in it. This is called a null value. In the EMPLOYEES table, only those employees who have the role of sales representative have a value in the COMMISSION_PCT (commission) field.
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Последний раз редактировалось Marley; 13.01.2010 в 16:16.
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  #22  
Старый 26.12.2009, 03:57
Marley Marley вне форума
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По умолчанию Relational Database Properties



Properties of a Relational Database

In a relational database, you do not specify the access route to the tables, and you do not need to know how the data is arranged physically.

To access the database, you execute a structured query language (SQL) statement, which is the American National Standards Institute (ANSI) standard language for operating relational databases. The language contains a large set of operators for partitioning and combining relations. The database can be modified by using the SQL statements.
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Последний раз редактировалось Marley; 13.01.2010 в 16:18.
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  #23  
Старый 26.12.2009, 03:57
Marley Marley вне форума
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По умолчанию Communicating with an RDBMS Using SQL



Structured Query Language

Using SQL, you can communicate with the Oracle server. SQL has the following advantages:

Efficient
Easy to learn and use
Functionally complete (With SQL, you can define, retrieve, and manipulate data in the tables.)
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Последний раз редактировалось Marley; 13.01.2010 в 16:19.
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  #24  
Старый 26.12.2009, 03:58
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По умолчанию Oracles Relational Database Management System



Oracles Relational Database Management System

Oracle provides a flexible RDBMS called Oracle Database 10g. Using its features, you can store and manage data with all the advantages of a relational structure plus PL/SQL, an engine that provides you with the ability to store and execute program units. Oracle Database 10g also supports Java and XML. The Oracle server offers the options of retrieving data based on optimization techniques. It includes security features that control how a database is accessed and used. Other features include consistency and protection of data through locking mechanisms.

The Oracle10g release provides an open, comprehensive, and integrated approach to information management. An Oracle server consists of an Oracle database and an Oracle server instance. Every time a database is started, a system global area (SGA) is allocated and Oracle background processes are started. The SGA is an area of memory that is used for database information shared by the database users. The combination of the background processes and memory buffers is called an Oracle instance.
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Последний раз редактировалось Marley; 13.01.2010 в 16:19.
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  #25  
Старый 26.12.2009, 03:58
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По умолчанию SQL Statements



SQL Statements

Oracle SQL complies with industry-accepted standards. Oracle Corporation ensures future compliance with evolving standards by actively involving key personnel in SQL standards committees. Industry-accepted committees are the American National Standards Institute (ANSI) and the International Standards Organization (ISO). Both ANSI and ISO have accepted SQL as the standard language for relational databases.


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Последний раз редактировалось Marley; 13.01.2010 в 16:20.
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  #26  
Старый 26.12.2009, 03:58
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По умолчанию Tables Used in the Course



Tables Used in the Course

The following main tables are used in this course:

EMPLOYEES table: Gives details of all the employees
DEPARTMENTS table: Gives details of all the departments
JOB_GRADES table: Gives details of salaries for various grades

Note: The structure and data for all the tables are provided in Appendix B.
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Последний раз редактировалось Marley; 13.01.2010 в 16:21.
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  #27  
Старый 26.12.2009, 03:58
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По умолчанию Summary



Summary


Relational database management systems are composed of objects or relations. They are managed by operations and governed by data integrity constraints.

Oracle Corporation produces products and services to meet your RDBMS needs. The main products are the following:
  • Oracle Database 10g, with which you store and manage information by using SQL
  • Oracle Application Server 10g, with which you run all of your applications
  • Oracle Enterprise Manager 10g Grid Control, which you use to manage and automate administrative tasks across sets of systems in a grid environment

SQL

The Oracle server supports ANSI-standard SQL and contains extensions. SQL is the language that is used to communicate with the server to access, manipulate, and control data.
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Последний раз редактировалось Marley; 13.01.2010 в 16:23.
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