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  • Java面试题—初级(7)

    作为一枚Java后端开发者,数据库知识必不可少,对数据库的掌握熟悉度的考察也是对这个人是否有扎实基本功的考察。特别对于初级开发者,面试可能不会去问框架相关知识,但是绝对不会不去考察数据库知识,这里收集一些常见类型的SQL语句,无论对于平常开发还是准备面试,都会有助益。

    基本表结构:

            student(sno,sname,sage,ssex)学生表
            course(cno,cname,tno) 课程表
            sc(sno,cno,score) 成绩表

            teacher(tno,tname) 教师表

     

    101,查询课程1的成绩比课程2的成绩高的所有学生的学号

    select a.sno from
    (select sno,score from sc where cno=1) a,
    (select sno,score from sc where cno=2) b
    where a.score>b.score and a.sno=b.sno
    

      

    102,查询平均成绩大于60分的同学的学号和平均成绩

    select a.sno as "学号", avg(a.score) as "平均成绩" 
    from
    (select sno,score from sc) a 
    group by sno having avg(a.score)>60
    

      

    103,查询所有同学的学号、姓名、选课数、总成绩

    select a.sno as 学号, b.sname as 姓名,
    count(a.cno) as 选课数, sum(a.score) as 总成绩
    from sc a, student b
    where a.sno = b.sno
    group by a.sno, b.sname

    或者:

    selectstudent.sno as 学号, student.sname as 姓名,
     count(sc.cno) as 选课数, sum(score) as 总成绩
    from student left Outer join sc on student.sno = sc.sno
    group by student.sno, sname
    

      

    104,查询姓“张”的老师的个数

    selectcount(distinct(tname)) from teacher where tname like '张%‘ 


    或者:

    select tname as "姓名", count(distinct(tname)) as "人数" 
    from teacher 
    where tname like'张%'
    group by tname
    

      

    105,查询没学过“张三”老师课的同学的学号、姓名

    select student.sno,student.sname from student
    where sno not in (select distinct(sc.sno) from sc,course,teacher
    where sc.cno=course.cno and teacher.tno=course.tno and teacher.tname='张三')
    

      

    106,查询同时学过课程1和课程2的同学的学号、姓名

    select sno, sname from student
    where sno in (select sno from sc where sc.cno = 1)
    and sno in (select sno from sc where sc.cno = 2)

    或者:

    selectc.sno, c.sname from
    (select sno from sc where sc.cno = 1) a,
    (select sno from sc where sc.cno = 2) b,
    student c
    where a.sno = b.sno and a.sno = c.sno
    

      

    或者:

    select student.sno,student.sname from student,sc where student.sno=sc.sno and sc.cno=1
    and exists( select * from sc as sc_2 where sc_2.sno=sc.sno and sc_2.cno=2)
    

      

    107,查询学过“李四”老师所教所有课程的所有同学的学号、姓名

    select a.sno, a.sname from student a, sc b
    where a.sno = b.sno and b.cno in
    (select c.cno from course c, teacher d where c.tno = d.tno and d.tname = '李四')
    

     

    或者:

    select a.sno, a.sname from student a, sc b,
    (select c.cno from course c, teacher d where c.tno = d.tno and d.tname = '李四') e
    where a.sno = b.sno and b.cno = e.cno
    

      

    108,查询课程编号1的成绩比课程编号2的成绩高的所有同学的学号、姓名

    select a.sno, a.sname from student a,
    (select sno, score from sc where cno = 1) b,
    (select sno, score from sc where cno = 2) c
    where b.score > c.score and b.sno = c.sno and a.sno = b.sno
    

      

    109,查询所有课程成绩小于60分的同学的学号、姓名

    select sno,sname from student
    where sno not in (select distinct sno from sc where score > 60)
    

      

    110,查询至少有一门课程与学号为1的同学所学课程相同的同学的学号和姓名

    select distinct a.sno, a.sname
    from student a, sc b
    where a.sno <> 1 and a.sno=b.sno and
    b.cno in (select cno from sc where sno = 1)
    

      

    或者:

    select s.sno,s.sname 
    from student s,
    (select sc.sno 
    from sc
    where sc.cno in (select sc1.cno from sc sc1 where sc1.sno=1)and sc.sno<>1
    group by sc.sno)r1
    where r1.sno=s.sno
    

      

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  • 原文地址:https://www.cnblogs.com/javazhiyin/p/8889031.html
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