關系模式
表格需求：
1.student表
| sno | sname | age | gender |
| 1 | liqiang | 23 | male |
| 2 | liuli | 22 | female |
| 3 | zhangyou | 22 | male |
2.course表
| cno | cname | teacher |
| k1 | c | wanghua |
| k5 | database | chengjun |
| k8 | complie | chengjun |
3.score表
| sno | cno | score |
| 1 | k1 | 83 |
| 2 | k1 | 85 |
| 5 | k1 | 92 |
| 2 | k5 | 90 |
| 5 | k5 | 84 |
| 5 | k8 | 80 |
問題：
1.用SQL語句實現如下檢索：
（1）查詢‘程軍’老師所教授的所有課程
select cname from course where teacher like 'chengjun';
（2）查詢‘李強’同學所有課程的成績
select course.cname,score from score,student,course wre here student.sno=score.sno and score.cno=course.cno and sname='liqiang';
（3)查詢課程名為‘C’的平均成績
select avg(score) from score where cno=(select cno from course where cname='c');
（4）查詢選修了所有課程的同學的信息
select sno from score group by sno having count(sno) >= (select count(cno) from course);
分析:該問題中首先是要對score表進行統計，統計出sno出現的次數，理論上sno的為學生所報的課程數，若該值等於course表中課程統計數量，即為結果。
（5）檢索王老師所授課程的課程號和課程名
select cno,cname from course where teacher like 'wang%';
（6）檢索年齡大於23歲的男學生的學號和姓名
select sno,sname from student where age > 23;
（7）檢索至少選修王老師所授課程中一門課程的女學生姓名
select distinct sname from student,score where score.cno in (select cno from course where teacher like 'wang%') and gender='female';
select sname from student,course,score where student.sno=score.sno and course.cno=score.cno and course.teacher like 'wang%' and student.gender='female';
(8)檢索李同學不學的課程的課程號
select cno from course where cno not in (select cno from rom score,student where student.sno=score.sno and sname like 'li');
（9）檢索至少選修兩門課程的學生學號
select sno from score group by sno having count(sno) > 2;
（10）檢索全部學生都選修的課程的課程號和課程名
select cno,cname from course where cno in (select cno from score group by cno having count(*) = (select count(*) from student));
思路解析：學生數量=score表中單科目總數
（11）檢索選修課程包含王老師所授課程的學生學號
select sno from score where cno in (select cno from course where teacher like 'wang%');
select distinct sno from score,course where score.cno=course.cno and teacher like 'wang%';
（12）統計有學生選修的課程門數
select count(distinct cno) from score;
（13）統計選修k1課程的學生的平均成績
select avg(score) from score where cno='k1';
（14）求王老師所授課程的每門課程的學生的平均成績
select avg(score),score.cno from score,course where course.cno=score.cno and teacher like 'wang%' group by score.cno;
（15）統計每門課程的學生選修人數（超過2人的課程才統計）。要求輸出課程號和選修人數，查詢結果按人數降序排列，若人數相同，按課程號升序排列。
select cno,count(sno) from score group by cno having count(sno) > 2 order by count(sno) desc,cno asc;
（16）檢索學號比李同學打，而年齡比她小的學生姓名
select sname from student where sno > (select sno from student where sname like 'liq%' ) and age < (select age from student where sname likke 'liq%');
（17）檢索姓名以li開頭的所有學生的姓名和年齡
select sname,age from student where sname like 'li%';
（18）在score中檢索成績為空值的學生學號和課程號
select sno,cno from score where score is null;
（19）檢索年齡大於女同學平均年齡的男學生姓名和年齡
select sname,age from student where age > (select avg(age) from student where gender='female') and gender='male';
（20）檢索年齡大於所有女同學年齡的男學生姓名和年齡
select sname,age from student where age > any (select age from student where gender='female');
（21）檢索至少選修程軍老師所授全部課程的學生姓名
select sname from student,course,score where student.sno=score.sno and course.cno=score.cno and teacher='chengjun' group by sname having count(*) >= (select count(*) from course where teacher='chengjun');
思路分析，首先找出選修程軍老師全部課程的學生，並統計該值在score表中出現的次數，該數字大於等於程軍老師教授課程總數量。