Showing posts with label rows. Show all posts
Showing posts with label rows. Show all posts

DAY-1: DEFINITION



What is Database?

A database is a collection of information organized into interrelated tables of data and specifications of data objects. Databases are designed to offer an organized mechanism for storing, managing and retrieving information. They do so through the use of tables. Database tables consist of columns and rows. Each column contains a different type of attribute and each row corresponds to a single record. For example, imagine that we were building a database table that contained Student_id, Name, Program_id, City, Division and Country.

Then we have simply start adding rows underneath those columns that contained the data we were planning to store. See the below schema and data table as per above discussion. This example will clear your concept of the relation between schema and data tables.

Schema:
Entity/Field Name
Data-Type
Student_id
Number(10)
Name
Varchar2(30)
Program_id
Varchar2(15)
City
Varchar2(15)
Division
Varchar2(15)
Country
Varchar2(15)







                                                            Schema: 1

The above schema explains that the student_id must be number data type and it will take up to 10 (ten) digit. So, greater then or equal to 11 (eleven) digit numeric value will not accept as a Student_id.  The Name field will accept maximum 30 (thirty) character. And all the remaining entity will follow rules as shown in the Data-Type Column in the above schema. Schema represents the physical infrastructure of a database table where we may keep our necessary data.

Data Table:

Student_id
Name
Program_id
City
Division
Country
200819222
Adina
English
Noakhali
Chittagong
Bangladesh
200819223
Nishi
English
Noakhali
Chittagong
Bangladesh
200819224
Iasha
Physics
Bogura
Rajshahi
Bangladesh
200819225
Asha
Chemistry
Dinajpur
Rajshahi
Bangladesh
                                                            Table: 1

The above table contains some sample data. We may easily understand that the all the data kept in above table are interrelated. The data belongs to students of an Institute. We may easily understand and get some information of a particular student by examining the records. Click here to see more examples of Insert Command, which will help to you learn of insert/store Value to a table.


What is Table?

A table in a relational database is a predefined format of rows and columns that define an entity. Database tables are composed of individual columns corresponding to the attributes of the object. A database may consist of many tables. In the above schema, student is an object. Student_id, name and etc are the entity. Entities are represents in column wise.  All the values of the entity are represents row wise as like above Data-Table. So, we may say finally that table is used to keep the records.

What is Record?

A database record consists of one set of tuples (variable/entity) for a given relational table. In a relational database, records correspond to rows in each table. In a relational database, a row consists of one set of attributes (or one tuple) corresponding to one instance of the entity that a table schema describes. The Schema 1 describes the tuples of student table and the table 1 shows the data of student table which correspondence the record of each student. Each record at table 1 illustrates row wise. In simply, a collection of fields is called a record.

What is Object?

A single data item related to a database object. The database schema associates one or more attributes with each database entity.

What is Field?

In database systems, fields are the smallest units of information you can access. In spreadsheets, fields are called cells. In database management systems, a field can be required, optional, or calculated. A required field is one in which you must enter data, while an optional field is one you may leave blank. A calculated field is one whose value is derived from some formula involving other fields. You do not enter data into a calculated field; the system automatically determines the correct value.

What is Attribute?

In database management systems, the term attribute is sometimes used as a synonym for field. In database systems, a field can have various attributes. For example, if it contains numeric data, it has the numeric attribute. Most fields have certain attributes associated with them. For example, some fields are numeric whereas others are textual, some are long, while others are short. In addition, every field has a name, called the field name.

What is data?

Data is a distinct piece of information, usually formatted in a special way. All software is divided into two general categories: data and programs. In Table 1, “200819222” is found in a row (cell). It is actually data. It indicates that is an Id of a student.

What is data files ?

In database management systems, data files are the files that store the database information, whereas other files, such as index files and data dictionaries, store administrative information, known as metadata.

Now, let us concentration on the  parts of SQL, which will be path of understanding SQL commands. Click Here to Visit Day-2 for these.



Popular Posts