北大“數(shù)據(jù)庫原理”上機實踐題目總結(jié)（6）

答案：2_1
    set talk off
    clear
    use teacher
    list off
    ？
    use teacher
    average age for sex =“女” to 22
    ？“女教師的平均年齡：”
    ？？22
    ？？“歲”
    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
    ？“課程總數(shù)：”
    ？？str（a）
    ？？“門”
    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