Insert into s 1 Select the author's name and count the number of books from the books connected by the author. author . authorized = books . authorized group by author ' s name，count > =3

Select left (student number, 4) as the grade, and course id and avg (grade) as the average value of tGrade.

The grouping is to the left (student number, 4), and the course id is to the left (student number, 4) desc.