In SQL, a primary key is a unique identifier that is used to identify each row of data in a table. It is a column or a set of columns that has a unique value for each row in the table, and is used to enforce data integrity and ensure that there are no any duplicate records in the table.
If you want to generate a primary key, you should include a PRIMARY KEY constraint when you create or change a table.
A primary key can be created in SQL when a table is created, or it can be added to an existing table using the ALTER TABLE statement. The syntax for creating a primary key is as follows:
CREATE TABLE table_name
(
column1 datatype PRIMARY KEY,
column2 datatype,
column3 datatype);
1. Definition of Primary Key
Each row in a table can be uniquely identified by its primary key, which might be a single column or a group of columns. The qualities of a primary key include the following:
Uniqueness: No two rows can have the same value in the primary key column(s).
Non-null: The main key column or columns must contain a value for each row.
Single value: A primary key must consist of a single value (although, in some cases, it may be composed of multiple columns, known as a composite key).
Indexing: The primary key automatically creates a unique index for the column(s), which helps speed up query performance.
2. Primary Key in the Blogging Database:-
A blogging program usually contains a number of things, including categories, posts, comments, and users (writers). The primary key for each of these entities will be unique.
