分享整理的12条sql语句连同数据

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俺觉得自 己试着写写sql,调试调试还是有帮助的,读人家sql例子好像读懂了,自己写就未 必思路正确,调试得通,写得简洁。 跟着网上流行的学生选课表的例子复习了一下: //www.jb51.cc/article/30655.htm 这篇文字在网上被转载烂了,里面有些sql适合用在应用系统里,有些“报表”的感 觉更重些,主要是想复习前者。前20条大体还挺好,后30条明显偏报表风格了,而 且后面选例良莠不齐,选了12个例子做练习,(其实很多语法,case,any/all,union之类的都没包括),用MysqL数据库,并共享自己造出来的数据。关于这12条 sql,修正了原文中有纰漏的地方。 sql是基本技能,若能写得好也挺精彩的,还在继续练习。绝不提倡努力写复杂sql 解决业务问题。应用系统里如果存在很复杂的sql,往往揭示了业务逻辑向下泄露 到sql层的问题,不利于维护和扩展,虽然这样确实常能提高运行效率。具体情况 自行取舍。
下面的例子都是比较通用的sql,其实针对特定的数据库,需要学的也挺多,比如 oracle db的decode函数,rowid,rownum,connect by 虽然不通用,但是很实用。 数据可以在这里下载,只是用作练习,没做任何外键关联:http://xiazai.jb51.cc/database/20120626051553698.txt 整理的sql在下面:
Student(S#,Sname,Sage,Ssex) 学生表
Course(C#,Cname,T#) 课程表
SC(S#,C#,score) 成绩表
Teacher(T#,Tname) 教师表 1. 选出每门功课都及格的学号
select distinct s# from sc where s# not in (select s# from sc where score <60)
2. 查询“1”课程比“2”课程成绩高的所有学生的学号;
SELECT c01.s# from (select s#,<a href="/tag/score/" target="_blank" class="keywords">score</a> from sc where c#=1) c01,
(select s#,<a href="/tag/score/" target="_blank" class="keywords">score</a> from sc where c#=2) c02
where c01.s# = c02.s# and c01.score > c02.score
3. 查询平均成绩大于60分的同学的学号和平均成绩;
select s#,avg(score) from sc group by s# having avg(score) > 60
4. 查询所有同学的学号、姓名、选课数、总成绩;
select student.s#,student.Sname,count(c#),sum(score) from student left outer join sc on student.s# = sc.s# group by student.s#,sc.s# 5.查询没学过“叶平”老师课的同学的学号、姓名;
select student.s#,student.Sname from student where student.s# not in (select distinct(sc.s#) from teacher,course,sc where Tname='叶平' and teacher.t# = course.t# and sc.c#= course.c# )
6. 查询学过“001”并且也学过编号“002”课程的同学的学号、姓名
select student.s#,student.sname from student,sc where student.s# = sc.s# and sc.c# = 1 and exists (select from sc sc_2 where sc_2.c#=2 and sc.s#=sc_2.s#)
7. 查询学过“叶平”老师所教的所有课的同学的学号、姓名 (巧妙)
select s#,sname from student where s# in
(select s# from sc,teacher,course where tname='叶平' and teacher.t#=course.t# and course.c#= sc.c# group by s# having count(sc.c#)=
(select count(c#) from teacher,course where tname='叶 平' and teacher.t#=course.t#) ) 8. 查询课程编号“002”的成绩比课程编号“001”课程低的所有同学的学号、姓名 (有代表性)
select s#,sname from (select student.s#,student.sname,score,(select score from sc sc_2 where student.s#=sc_2.s# and sc_2.c#=2) score2 from student,sc where
sc.s#=student.s# and sc.c#=1) s_2 where score2 < score
9.查询没有学全所有课的同学的学号、姓名
select student.S#,Sname from student,sc where student.s# = sc.s# group by s#,sname having count(c#) < (select count(c#) from course) 10. 查询至少有一门课与学号为“002”的同学所学相同的同学的学号和姓名;
select distinct(sc.s#),sname from student,sc where student.s#=sc.s# and c# in (select c# from sc where s#=002)
11. 把“SC”表中“叶平”老师教的课的成绩都更改为此课程的平均成绩; update sc inner join
(select sc2.c#,avg(sc2.score) score from sc sc2,course where
sc2.c#=course.c# and tname='叶平' and teacher.t# = course.t# and course.c#=sc2.c# group by course.c#) sc3 on sc.c#=sc3.c# set sc.score=sc3.score
12. 查询2号的同学学习的课程他都学了的同学的学号;(注意理解:where语句的 第一个条件过滤掉不满足c#的记录,再group by,就比较清晰)
select S# from SC where C# in (select C# from SC where S#=2)
group by S# having count(
)=(select count(*) from SC where S#=2); 作者 人在江湖

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