What database behavior of PostgreSQL is observed if no explicit action is specified when deleting a record that is linked to another table via a foreign key?

In PostgreSQL, if no explicit action is specified when deleting a record related to another table via a foreign key (for example, ON DELETE CASCADE or ON DELETE SET NULL), the default behavior is ON DELETE NO ACTION.

This means that an attempt to delete a record that is referenced from another table will result in a foreign key constraint error, and the deletion will not be performed.

Thus, the database prevents data integrity violations by not allowing the deletion of a parent record while related child records exist.

Example:

-- Orders table with a foreign key to the customers table
CREATE TABLE customers (
    id SERIAL PRIMARY KEY
);

CREATE TABLE orders (
    id SERIAL PRIMARY KEY,
    customer_id INT REFERENCES customers(id)
);

-- Attempt to delete a customer with existing orders without ON DELETE CASCADE
DELETE FROM customers WHERE id = 1; -- will cause an error

To allow deletion with automatic removal of related records, you need to explicitly specify ON DELETE CASCADE when creating the foreign key.