What Is Database ?

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SQL What Is Database ?

Database is a software that simply stores information. Most software can store information, but the difference is that the database can manage and change this information efficiently and quickly. The database is the heart of the information system and gains value through effective use. It is essential to access information when necessary.


When you think that a library without index and all books have the same cover, you can imagine how much work the library users will have. A database is the perfect index system of a library, but it is also the library itself. Relational database management systems relational database management systems - rdbms are programs in which large amounts of data can be securely held, provided with fast access to information, information can be kept in integrity, and multiple users can access information simultaneously. Oracle database is also a relational database management system.


What Is Database ?

In the simplest sense, the database is all records and files organized for a specific purpose. You may have collected the names and addresses of your friends or customers on your computer system. Maybe you collect all the letters you write and arrange them according to the recipient. You may also have a group of files in which you collect your financial data such as debit and balance of your accounts or checkbook for payment and collection. Word processing documents that you organize according to their subjects are, in the broadest sense, a kind of database. Spreadsheet files that you organize by use are also a separate type database. All program shortcuts on the Windows Start menu are also a database. It is a database of Internet shortcuts arranged in the Favorites folder.


If you are very organized, you can manage several hundred spreadsheets or shortcuts using folders and subfolders. When you do this, you become the database administrator. What are you going to do as the problems you're trying to solve grow? How can you easily gather information about all customers and their orders when data is stored in various documents or spreadsheets? How can you maintain links between files when you enter new information? How do you make sure the data is entered correctly? What do you do when you need to share your information with many people and don't want two people trying to update the same data at the same time? If you have experienced such difficulties, you need a database management system (DBMS).


The purpose of the databases is to process large amounts of corporate data. The data is stored in an electronic format on a regular basis. This information, which is regularly backed up and checked, is made available to a large number of applications and users. One of the most important features of databases is the ability to quickly and securely convert large amounts of data into the information needed.


  • A database is a collection of data organized in a specific field and related to each other.
  • A database is a system for organizing, storing and querying a large set of related data used by many users.
  •  A database is a collection of data that stores associated data, except harmful and unnecessary data, to serve many applications.
  •  Database is a computer based record keeping system. The purpose of the system is to record and maintain data.
  •  The database provides centralized control of data in an organization.
  •  The database system is simply a computerized record tracking system.


Nowadays, there are not many application programs that do not use any database management system. Due to this demand, many database management systems have emerged. Some of them are Microsoft Access, Microsoft SQL Server, Oracle, Sybase. The most important common feature of these databases is that they include relational database technology.


Database Types

Distiributed Databases

Databases stored in multiple physical environments are called shared databases. There are two basic ways to share a database. The first way is to partition the central database. Thus, each remote processor has the necessary data to serve its own local area. In the second path, the central database is copied to all remote points.

Object-Oriented Databases

A database that automatically animates drawings, graphics, images, photos, sounds, and all motion video representations and stores them as objects to share. This database is used in the field of finance and marketing. Reason; The most appropriate response to the changes in the economic conditions of finance and marketing storage system is the object-weighted database.

Hypermedia Databases

The user can choose his own path to switch from module to module. The information scheme does not require a predetermined organizational chart. Each module can be displayed on the screen and can also show the connections between the module shown and other database modules.

Multidimensional Data Analysis

This analysis allows the user to see the same data in many different dimensions. For example, in Central Anatolia, Aegean and Marmara regions, a company that sells four different products such as nuts, bolts, plumbing and screws can be used to see their actual sales.

Data Banks

Database software that stores integrated, current and historical data in accordance with the expectations of all personnel in the enterprise is called Data Banks. Data compiled from the internal and external sources on an instant, hourly, daily, weekly or monthly basis are copied in the database. These data are standardized and integrated in such a way that they can be easily used in management initiatives of different units of the enterprise. Anyone who attempts can access the database but cannot make any changes.


Database Queries

Physical design is completed with actual data entry and trials. Database systems undergo continuous changes due to technological changes and changes in users' requirements. At the end of a certain period, as they do, they lose their actuality and end their lives. The most important process performed on database systems is querying. A single table can be used for querying, and multiple tables can be queryed diagonally, depending on the relationship between them. For querying, QBE (Query By Example) or SQL (Structured Query Laguage) tools are used. These tools are often provided as part of the above-mentioned database operating system.


Database Design

A database design is performed in two phases; the first is Logical Design and the second is Physical Design. While the database that will use logical design consists of the works performed independently of the operating system, the objects that occur in the logical design in physical design are realized by using a database operating system.


Phases of Logical Design


  •  Identification of the problem,
  •  Examination of the system in use, and finding movements within the system,
  •  Identifying the needs of the database users,
  • Determination of the assets and characteristics of the database,
  •  Determination of the reports to be created,
  • Normalization of tables.


Physical Design Phases


  •  Creation of assets,
  •  Realization of form design and data entry,
  •  Adapting the report design,
  •  Writing support programs and user interface to facilitate database usage
  •  Testing the database system and preparing documents.


Relational Databases

Nearly all modern database management systems store and process information using the relational database management model. The relational term arises from the fact that each record in the database contains information about a single topic and only related to that topic. If you examine the relational database management model, you will see that the relationship term applies only to a rowset related to a topic. In addition, data related to two classes of information (such as customers and orders) can be managed as a whole, depending on the associated data values. For example, it is unnecessary to store customer name and address information with each order the customer places. In a relational database system, there is a field that stores information about orders, such as a customer ID, to link each order to the appropriate customer information.


In Relational Database Management System (RDBMS), the system manages all data in tables. Tables store information about a topic (such as customers and products). However, there are columns with other relevant information (for example, customers' addresses or book titles), and rows that describe all the attributes of a single instance (for example, data about a particular customer or book). Even when we query the database (retrieving information from one or more tables), the result is always something similar to another table.


You can also merge the associated values ​​from multiple tables or queries. For example, you can combine author and book information to find out which authors are writing which books. You can combine employee and contract information to find out which salesperson deserves a premium.


Relational database management system regulates the structure of databases. This feature makes it possible to:


  •  Ensures accurate and efficient storage of data.
  •  Relational integrity rule is provided.
  •  Allows you to recover data when the system crashes through change records.


The aim of the relational database model is high efficiency. For example, suppose we keep staff information in a database. Personnel name, address and telephone information will be reproduced for the different departments where the personnel work. This unnecessary redundancy leads to both increased disk space requirements and increased data access time issues when dealing with a significant number of databases. In the relational model, the data will be divided into two tables. The first table contains personal information such as insurance number, identification number, address, telephone, age. The second table contains the information of the department where the personnel work instead of duplicating this information.


Database Skills

The relational database management system (RDBMS) allows you to fully control the identification, working with, and sharing of your data. The system offers advanced features that make it easy to catalog and manage a large number of data in many tables. RDBMS has three main capabilities: defining, managing, and controlling data.


  •  Defining Data: You can define which data is stored in the database, the data type (for example, numbers or characters), and how the data is associated. In some cases, you can define how data should be formatted and validated.
  •  Data Management: You can work with data in many ways. You can select which data fields you want, filter and sort the data. You can combine (summarize) data with associated information. You can select an information set and ask RDBMS to update it, delete it, copy it to a separate table, or create a new table that contains this data.
  •  Data Control: You can define who can read, update, or add data. In most cases, you can also define how multiple users share and update data.


All of these functionality are included in the powerful features of Microsoft Access. Now let's look at how Access accomplishes these skills and compare it to what you can do with spreadsheet or word-processing programs. Microsoft Access is a fully functional RDBMS. It provides all of the data identification, management, and auditing features you need to manage a large number of data.


Data Identification and Storage

When you work with a document or spreadsheet, you are usually completely free to identify the content of the document or any cell within the spreadsheet. You may have added more than one column of text, paragraphs, tables, graphics, or multiple fonts displayed on a given page in a document. In a given column in a spreadsheet, you can have the textual data above to define a column heading for printing or displaying, and you can apply various numeric formats within the column, depending on the function of the row. You need this flexibility because your word processing document must be able to carry your message to a written page content and store the data you analyze in your spreadsheet, as well as calculate and provide a presentation of the results.


This flexibility is great for solving relatively small, well-defined business problems. However, when a document exceeds several dozen pages, it becomes difficult to control it and when a spreadsheet exceeds several hundred lines of information. As the amount of data increases, you may find that you have exceeded the storage limits of your word processing or spreadsheet program or computer system. If you design a document or spreadsheet to be used by others, it is very difficult, but not impossible, to control how they use the data or how they enter new data. For example, a user can inadvertently enter character data when a date value is entered in one cell and a currency value is entered in order to make sense in a spreadsheet. Some spreadsheet programs allow you to define a "database" field within the spreadsheet. This is to help you manage the information you need to achieve the desired result. However, you can still be blocked by the basic storage limits of the spreadsheet program, and you do not have enough control over what is entered in the columns and rows of the database area. You may also find that your spreadsheet program doesn't recognize things like pictures and sounds if you need to go beyond number and character data.


An RDBMS allows you to define the data type and storage format you have. Generally, you can also define the rules that RDBMS can use to ensure the integrity of your data. In its simplest form, a validation rule ensures that you do not accidentally store alphabetic characters in the field that must contain numbers. Other rules can define valid values ​​or ranges of values ​​for your data. On the most complex systems, you can define the relationship between data collections (usually tables or files) and ask RDBMS to ensure that the data remains consistent. For example, you can have the system automatically check that each order has been entered for a valid customer.


Defining your data with Access (such as text, number, date, time, currency, internet connections, picture, sound, document and spreadsheet); You are completely free to define how Access stores your data (string length, number-sensitive, and date / time-sensitive), and to define what it looks like when you view or print data. You can define simple or complex validation rules to ensure that only the correct values ​​exist in the database. You can ask Access to check that there are valid relationships between files or tables in the database.



SQL (Structured Query Language)

SQL is known as the standard programming language of database management systems. It is possible to use the SQL language in query windows or in Visual Basic programs within a Microsoft Access program.


SQL commands can be grouped under two headings:


  •  DDL Commands (Database definition language)
  •  DML Commands (Data processing language)


DDL Commands

Create table : Creates the fields and indexes of a new table.

Create index : Indexes the specified table.

Drop table : Deletes the specified table and indexes from the database.

Alter table : Adds new fields to the table and allows you to change the field definitions.

DML Commands:

Select : Enables selection of records in the table according to the specified criterion.

Insert :  Inserts a new record into the table.

Update : Updates the fields of the specified record.

Delete : Deletes the specified records.


These commands cannot be used alone. Some helper expressions are needed to implement functions:


From : Defines the table from which to query.

Where : Defines the criterion to be used at the time of the query.

Group By : Groups records according to specified area.

Having : Defines the criterion that each group must meet.

Order By : Enables sorting of selected records.

Constraint : Provides index definition and relationship with another table.


Most Famous Database Systems


  •  PostgreSQL
  •  MsSQL
  •  MySQL
  •  Oracle
  •  Sybase
  •  BerkeleyDB
  •  DB2
  •  Microsoft Access
  •  Informix
  •  Interbase
  •  Sysbase
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