Difference Between Primary Key And Unique Key Explained!

  • What is the need for a key in the database?
  • What is a Primary Key?
  • What is a Unique Key?
  • Primary Key Vs Unique Key

What is the need for a key in the database?

What is a Primary Key?

  • A primary key is a key in a relational database that is selected by Database Administrator as a primary means to uniquely identify a tuple or row in a database table.
  • A primary key can also be defined as that candidate key of the relational table which is selected by the Database Administrator as a primary means to uniquely identify a tuple or row in a database table.

Features Of Primary Key

  • It doesn’t allow duрliсаte vаlues.
  • It can be made from one or more columns of the table.
  • It doesn’t allow NULL value.
  • Only a single primary key per table is allowed.
  • It imрlements the entity integrity оf the tаble.

What is a Unique Key?

  • The unique Key is very similar to the primary key except for the fact that the primary key doesn’t allow null values in the column but the unique key allows null in the column. So Unique key can be defined as a unique identifier for rows in a database table that doesn’t allow duplicate value and can uniquely identify a row/tuple in the database table. We can make Unique Key from one or more table fields.
  • It is used to enforce unique constraints on a column and a group of columns which is not a primary key. Now let’s again consider the Employee Table :

Features Of Unique Key

  • Unique Keys can be made from one or more columns.
  • Multiple Unique keys per table are allowed.
  • It is in non-clustered unique indexes by default.
  • It allows NULL value, but only one NULL is allowed per column

Primary Key Vs Unique Key

Summing up…

  1. Key Constraints In RDBMS: Difference Between Primary Key And Foreign Key
  2. What Is Regression In Data Mining?
  3. Most Common Programming Interview Questions With Answers 2022
  4. Top 50 OOPs Interview Questions With Answers 2022

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