Primary key in the database

Primary key: A table often has a combination of columns or columns whose values uniquely identify each row in the table. Such a column or columns is called the table's primary key, which enforces the entity integrity of the table. When you create or change a table, you can create a primary key by defining the PRIMARY key constraint. A table can have only one PRIMARY key constraint, and a column in the PRIMARY key constraint cannot accept null values. Because the PRIMARY KEY constraint ensures unique data, it is often used to define identity columns. Role: 1) Ensure the integrity of the entity; 2) speed up the operation of the database 3) when you add a new record to a table, Access automatically checks the primary key value of the new record and does not allow the value to repeat with the primary key values of other records. 4) Access automatically displays the records in the table in the order of the primary key values. If no primary key is defined, records in the table are displayed in the order in which they are entered.

Primary key in the database