Please help me understand this Question

hi all

i have a question to ask,

how do i implement an extra mandatory constraint that a company must have one or more students.
By considering inserting a new company, and deleting students, also consider updating a student who is moving between companies.

how do i do it in PL/SQL prosedure and triggers?

Sounds like a complex enough constraint to enforce with procedures.

You check for the condition, and explicitly raise the exception.

e.g.

IF <Error Condition> THEN
RAISE_APPLICATION_ERROR(-20001,
'<Error Message>');
END IF;