1. Write a function to calculate the GPA of a student.
2. Write a trigger to check and enforce the following constraints when a new record is inserted into the course table: The course prerequisite relationship is hierarchical up to three levels.
3. Write a procedure to merge two sections of the same course. All students enrolled in one section will be added into the other section. The empty section will then be dropped. Data about the meeting days and textbooks of the empty section need to be deleted. The section numbers of the sections after the dropped section need to be adjusted accordingly. Note that the number of students enrolled in a section cannot exceed the number of seats of the section by more than 10%.