What happens if an administrator tries to execute the SQL query DELETE FROM Users WHERE user_id = 5, assuming the user with ID=5 has tasks in the Tasks table? Consider a classic relational database (PostgreSQL/MySQL).

If in a classical relational database (PostgreSQL or MySQL) the Tasks table contains foreign keys referencing the Users table, and there are related records in Tasks for the user with user_id = 5, then attempting to execute the query:

DELETE FROM Users WHERE user_id = 5;

will result in different behaviors depending on the foreign key settings:

• If the foreign key is set with ON DELETE RESTRICT (default) — deletion will be prohibited, and the database will return an error because related records exist.

• If the foreign key is set with ON DELETE CASCADE — all related tasks in Tasks will be deleted, and then the user will be deleted.

• If the foreign key is set with ON DELETE SET NULL — the user_id field in related Tasks records will be set to NULL.

If foreign keys are not set, the user deletion will occur, but the Tasks records will remain, leading to "dangling" references (violation of data integrity).

Thus, the behavior depends on the integrity constraints defined in the database schema.