what is a primary key

A primary key is a special relational database table column (or combination of columns) designated to uniquely identify all table records.

Here are the steps to understand what a primary key is:

1. Understanding Databases: A database is a structured set of data. So, a primary key is a field in a table which uniquely identifies each rows/records in a database table.

2. Uniqueness: Primary keys must contain unique values. A primary key column cannot have NULL values. This means that the primary key value is always unique and never null in any given table.

3. Primary Key Function: A primary key’s main features are: it must contain a unique value for each row of data. It cannot contain null values. By defining a primary key on your table you are ensuring that you will not have duplicate rows in your table.

4. Composite Key: When more than one columns are used as a primary key, it is known as composite key.

5. Example: For example, in a student database, we cannot determine a record for a student uniquely on the basis of a student name as two students can have the same name. If we have a 'Student ID' column, which is unique for every student, then 'Student ID' can be a primary key.

6. Importance: Primary keys are important when designing a database because they provide a way to uniquely identify each record, allow efficient access to data, ensure data integrity, and help establish relationships between tables.