答案：2_1
set talk off
clear
use teacher
list off
？
use teacher
average age for sex =“女” to 22
？“女教师的平均年龄：”
？？22
？？“岁”
答案：2_2
set talk off
clear
use c2
index on cxi to 11
total on cxi to 12 fields ctimes
use 12
list fields ctimes，cxi for cxi=“物理” off
？
use cc
index on cname to 14
total on cname to 15 fields sum
use 15
note list fields sum ，cxi off
note？
sum sum to a
？“课程总数：”
？？str（a）
？？“门”
答案：2_3
set talk off
clear
select teacher.tno，c2.cname，c2.ctimes，sum（c2.ctimes）；
from teacher，c2，tc；
where teacher.tno=tc.tno and c2.cno=tc.cno and teacher.tno='1000'；
group by c2.ctimes
答案：2_4
set talk off
select teacher.tno，teacher.tname，avg（tc.grade）；
from teacher，tc；
where teacher.tno=tc.tno ；
group by teacher.tno；
order by tc.grade
set talk off
close all
return