- The column or columns of the table whose value uniquely identifies each row in the table is called primary key.
- You can define column as primary key using primary key constraint while you create table.
- When you define a column as primary key, a unique index is created which restricts duplicate data and fast access to data.
- A column defined as primary key doesn’t allow null value.
- By default, clustered index in created with the column having primary key.
- Unique key also ensures data uniqueness like primary key.
- A column with unique key defined allows null value.
- By default, it creates non-clustered index.