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Composite Key
A composite key is also called a composite primary key. It refers to a combination of two or more fields that
can uniquely identify or retrieve records. For example, the STU_ID and the AADHAR fields in a student table
can be used as a Composite key to uniquely identify each record in the table.
Foreign Key
The main table of a database is referred to as the ‘Master Table’ and the tables in which the related data is
stored are referred to as ‘Transaction Table’. The tables are related and are linked through a field which is
common. This common key field in the transaction table is called the ‘Foreign key’ and its value depends
on the primary key values of the master table. The foreign key identifies a column or set of columns in one
(referencing) table that refers to a column or set of columns in another (referenced) table.
Table: Teacher Table: Student
Primary key Foreign key
Primary key
STU_ID STU_NAME SUBJECT T_ID
T_ID TEACH_NAME 101 Mohit Accounts 2
1 Mr. Hemant 102 Ankur IP 1
2 Mr. Lavish 103 Dev Maths 3
3 Ms. Shreya 104 Rashi Accounts 2
Primary Key: Teacher- T_ID, Student – STU_ID
Foreign key: Student- T_ID
In Teacher table, the primary key is T_ID. In Student table, the primary key is STU_ID. The relationship between
Teacher and Student is made because of the presence of a common field T_ID. So T_ID is a Primary key in
table Teacher and a Foreign key in table Student.
DATABASE OBJECTS
There are different objects that help in executing the purpose of database package.
Tables: A table is the basic element of a database in which data is kept in columns (called Fields) and rows
(called Records). It acts as a container that stores data pertaining to a single object, subject or purpose.
Queries: Queries are commands that are used to define the data structure and also to manipulate the
data in the database. It is a call or a request to generate some information from the database. We can use
queries to extract specific data from one or more tables based on our needs.
Forms: Form provides an interface in a user-specified layout, which lets the user to view the data or enter
new data or to modify the existing data records directly in database objects such as tables. Form provides
graphical elements such as text boxes, drop-down menus, check boxes and buttons that users can use to
add data, edit data and deleted data, etc. By using forms, users can efficiently manage database operations
without needing to write queries.
Reports: Report displays the information in a format as per user’s need. It is used to view and print
information. They provide a concise and meaningful summary of information. Reports can be updated only
if the data is changed or added to a table or query based on which it is created.
Introduction to Database Management System 213

