What is primary key in DBMS | Benefits, Properties and Uses

Summary: In this tutorial, we will learn What is Primary key in SQL, and also we will understand the Primary Key(FK) properties, uses, and there benefits in DBMS. Furthermore, the Primary key is a SQL constraint that helps us to manage the data and avoid any invalid transactions on it. let’s understand the What is Primary Key in detail.

What is primary key in DBMS?

A primary key, also known as a primary keyword, is a key in a relational database that’s unique for every record. It is a unique identifier, like a passport number, Mobile number (including area code), GST Number, or vehicle identification number (VIN). Furthermore, a relational database must always have only one PK. PK usually appear as columns in relational database tables.

• A PK is a field in a table that uniquely identifies each row/record in a database table. Primary keys always contain unique values. A PK column can’t have NULL values.
• A table can have only one PK, which may consist of single or multiple fields. Thus, when multiple fields are used as a PK, then they are known as composite keys.
• If a table has a PK defined on any field(s), then you can’t have two records having the same value of that field(s).

Properties and Rules of an SQL Primary Key?

• The PK enforces the entity integrity of the table.
• The PK must contain unique data.
• A PK length can’t be exceeded 900 bytes.
• A PK can not contain a null value.
• It can not contain the duplicate value for a PK.
• A table can contain only one primary key (PK) constraint.

Understand The Example

Imagine you have an EMPLOYEES table that contains a record for each Employee at a Company. The Employee’s unique Employee ID number is a good choice for a primary key in the EMPLOYEES table. The Employee’s first and last name are not good choices because there is always the chance that more than one Employee might have an identical name.

Other bad choices for primary keys include email address, ZIP code. Furthermore, all of these can change or represent many people. Thus, The identifier used as a PK must be unique.

Tips: Always Choosing Good Primary Keys

When you select the correct PK, database lookups are speedy and reliable. simply remember:
Use a Number. for the PK whenever possible. SQL Server or other DBMS process number data types faster than character data types.
Never Modification. the PK after you assign it.
Keep It Short. Because the PK is used for lookups & comparisons, a short primary key means the DBMS can process it more quickly than a long PK.
Keep It Easy. do not use any special characters, embedded spaces, or a mixture of upper and lower capitalization.

What Are the Benefits?

The main advantages are:
It uniquely identifies/recognized each row/record of a table
It gets a unique index for every PK-primary key column that helps with faster access