A foreign key is specified as a key which is related to the primary key of another table. A relationship needs to be created between two tables by referencing foreign key with the primary key of another table. Foreign key acts like a cross-reference between tables as it refers to the primary key of other table and the primary key-foreign key relationship is a very crucial relationship as it maintains the ACID properties of database sometimes.

A unique key is a single or combination of fields that ensure all values stores in the column will be unique. It means a column cannot stores duplicate values. This key provides uniqueness for the column or set of columns. For example, the email addresses and roll numbers of student's tables should be unique. It can accept a null value but only one null value per column. It ensures the integrity of the column or group of columns to store different values into a table.

Primary key and unique key both are the essential constraints of the SQL, but there is a small difference between them

Primary key carries unique value but the field of the primary key cannot be Null on the other hand unique key also carry unique value but it can have a single Null value field.

A Database is an organized form of data. The database is the electronic system which makes data access, data manipulation, data retrieval, data storing and data management very easy and structured. Almost every organization uses the database for storing the data due to its easily accessible and high operational ease. The database provides perfect access to data and lets us perform required tasks.

The Database is also called a structured form of data. Due to this structured format, you can access data very easily.

DBMS stands for Database Management System. This is a program which is used to control them. It is like a File Manager that manages data in a database rather than saving it in file systems.

Database management system is an interface between the database and the user. It makes the data retrieval, data access easier.

Database management system is a software which provides us the power to perform operations such as creation, maintenance and use of a data of the database using a simple query in almost no time.

Without the database management system, it would be far more difficult for the user to access the data of the database.

There are four types of database:

• Hierarchical databases (DBMS)
• Relational databases (RDBMS)
• Network databases (IDMS)
• Object-oriented databases

RDBMS is one of the most often used databases due to its easy accessibility and supports regarding complex queries.

RDBMS stands for Relational Database Management System. It is a database management system based on a relational model. RDBMS stores the data into the collection of tables and links those table using the relational operators easily whenever required. It facilitates you to manipulate the data stored in the tables by using relational operators. Examples of the relational database management system are Microsoft Access, MySQL, SQLServer, Oracle database, etc.

Normalization is used to minimize redundancy and dependency by organizing fields and table of a database.

There are some rules of database normalization which commonly known as Normal From and they are:

• First normal form(1NF)
• Second normal form(2NF)
• Third normal form(3NF)
• Boyce-Codd normal form(BCNF)

Using these steps, the redundancy, anomalies, inconsistency of the data in the database can be removed.

Normalization is mainly used to add, delete or modify a field that can be made in a single table. The primary use of Normalization is to remove redundancy and to remove the insert, delete and update distractions. Normalization breaks the table into small partitions and then link them using different relationships so that it will avoid the chances of redundancy.

The major disadvantages are:

• The occurrence of redundant terms in the database which causes the waste of the space in the disk.
• Due to redundant terms inconsistency may also occur id any change will be made in the data of one table but not made in the same data of another table then inconsistency will take place, which will lead to the maintenance problem and effects the ACID properties as well.