Why is a foreign key constraint needed? Can't we do without it?

A foreign key constraint is used to ensure referential integrity in a database. It guarantees that the value in a column (or set of columns) matches a value in the primary key of another table.

Without a foreign key:

• It is possible to accidentally insert a value that does not exist in the related table, leading to "broken" links.
• There is no automatic data integrity check at the database level.
• Maintaining the logic of relationships and cascade operations (delete, update) becomes more difficult.

Thus, a foreign key does not prohibit working without it, but its absence increases the risk of errors and complicates data maintenance. It helps the database automatically verify and maintain the correctness of relationships between tables.