What is a Primary Key

A primary key is a column or set of columns in a database table that uniquely identifies each record (or row) in that table. It serves as a unique identifier for the records, ensuring that no two rows can have the same value(s) for the primary key column(s). Here are some key points about primary keys:- 

1. Uniqueness:-  Each value in the primary key column(s) must be unique within the table. This means that no two records can have the same value for the primary key.

2. Non-null:-  Primary key values cannot be NULL. Every record in the table must have a value for the primary key column(s).

3. Indexing:-  Primary keys are typically indexed by the database management system (DBMS) for faster retrieval and efficient querying.

4. Enforcement of Data Integrity:-  Primary keys enforce entity integrity by ensuring that each record in the table is uniquely identifiable. They help maintain data accuracy and consistency by preventing duplicate records.

5. Relationships:-  Primary keys are often used in establishing relationships between tables. In relational database systems, primary keys are referenced by foreign keys in related tables to maintain referential integrity.

6. Definition:-  A primary key is typically defined when creating or altering a table using SQL (Structured Query Language). It can be defined as a single column or a combination of multiple columns.

For example, in a Customers table, a column named CustomerID might be designated as the primary key. Each customer record in the table would have a unique CustomerID value, allowing for easy and reliable identification of individual customers.