Terminology Related to Primary Key

What is a Primary Key?

A primary key in a table that uniquely identifies each row and column or set of columns in the table. The primary key is an attribute or a set of attributes that help to uniquely identify the tuples(records) in the relational table. The primary key provides the means to distinguish one tuple from all the others in the relation. It helps the user to identify the location and also the database system to identify, locate, and refer to one particular tuple in the relation....

Rules For Defining the Primary Key

Minimal: The primary key is composed of a minimum number of attributes that satisfy the unique occurrence of the tuples or records. So if one candidate key is formed using two attributes and the other using a single attribute then the one with a single attribute key should be chosen as the primary key. Accessible: The primary key is used to check the ability to access and interact with the database. The user must easily create, read or delete a tuple using it. NON NULL Value: The primary key which refers to a nonnull value that is required for the identification of the tuple (record) means that any attribute can not contain the non-null value in DBMS. Time Invariant: The values of the primary key must not change or become null during the lifetime of the relation. For example, we cannot choose the name attribute of the EMPLOYEE Relation as a primary key because there is no guarantee that two employees with the same name will never exist. Unique: The primary key in which value can not be duplicated in any of the rows or tuples of the relation....

Syntax For Creating and Deleting Primary Key

Let’s see what syntax is used for creating a table....

Understanding Primary Key

For Example, a table consists of columns EMP_ID, Name, PAN_NO, Salary, Dept. Below is the syntax for creating the Primary Key on the EMP_ID attribute of the EMPLOYEE table:...

Terminology Related to Primary Key

When it comes to primary keys, there are several related terminologies you may come across as follows:...

Advantages of Primary Key

Each line of a table is uniquely identified. This is very helpful when performing any operation on the data such as updating, deleting, searching, etc. Due to Primary key the access of records become faster....

Properties of Primary Key

A relation can contain only one primary key. A primary key may be composed of a single attribute known as a single primary key or more than one attribute known as the composite primary key. A primary key is also called a minimum super key. The attributes are not null in the primary key. Attributes that are part of the primary key are known as “prime attributes”. The primary key is always chosen from the candidate keys. The primary key attributes are irreducible. We use the convention that the attributes that form the primary key of the relation are underlined. The primary key cannot contain duplicate values....

Conclusion

In conclusion, in a database management system (DBMS), the primary key is the unique identifier for every record in the table, which guarantees data integrity and facilitates efficient data retrieval by uniquely identifying each record....

FAQs on Primary Key

Q.1: What is the primary key in SQL Server?...