All modern database management systems like SQL, MS SQL Server, IBM DB2, Oracle, My-SQL and Microsoft Access are based on Rdbms.
Rdbms was developed by a jermen scientice mr. E.F codd at 1970 this model was developed on the basis of a mathematical concept called relational algebra.
Relations are classified into three types, they are;
- 1:M or M:1
- M:M (many to many)
In this relationship one object have only one relation with another object.
In above image one employee have only one emp_id. this is the example of 1:1 relationship
one-many or many-one Relationship
In this relationship one object have relation with many other object.
In above image one faculty can teach many subjects. This is the example of 1:m relationship
In this relationship many object has the relationship with many other object.
In above image one customer can purchase many items and one item can purchase by many customers, this is the example of m:m relationship
Properties of Rdbms
- Data should be stored in the form of table.
- A table can be defined as collection of rows and columns
- The horizontal lines are known as row or tupples or record.
- The vertical lines are known as column or field or attributes.
- The intersection of row and column is known as cell.
- A cell is a place where you can store your data.
- The other name of table is called as entry or class or object.
What is table
Rdbms are use table to store data, table are the collection of related data entries and row and column. Below is the simple example of table which store detail about employee.
What is Field
Field is a smaller entity of the table which contains specific information about every record in the table. In the above example, the field in the Employee table consist of emp_id, name, salary.
What is row
Row is a part of table which is horizontally disply in table it is also called record. Row contains the specific information of each individual entry in the table. In below example row contain detail of Hitesh kumar records.
What is column
A column is a vertical entity in the table which contains all information associated with a specific field in a table.
What is cell
A cell is a place where you can store your data.