手写顺序
执行顺序
join语句
- 内连接：A、B表中共有的
- 左连接：A表中所有的
- 右连接:B表中所有的
-
左连接+条件：A中有B中没有的
-
右连接+条件 ：B中有A中没有的
-
全连接：A、B表中所有数据
- 全不连接：A、B表中各自独有的
sql语句
#试题一、找出平均成绩大于60的所有学生的学号（即student_id)、姓名和平均分数
SELECT a.`name`,a.student_id,AVG(b.number)
FROM tbl_student a,tbl_score b
WHERE a.student_id=b.`student_id`
GROUP BY a.student_id
HAVING AVG(b.number)>60
#试题二、查询所有学生的学号，姓名，选课数和总成绩；
SELECT a.`name`,a.student_id,COUNT(c.course_id),SUM(b.`number`)
FROM tbl_student a,tbl_score b,tbl_course c
WHERE a.student_id=b.`student_id` AND b.`course_id`=c.`course_id`
GROUP BY a.student_id
select a.student_id,b.name,COUNT(a.course_id),SUM(a.number)
from tbl_score a inner join
tbl_student b on a.student_id = b.student_id
GROUP BY a.student_id;
#试题三、查找名字中含“封”字的老师的总数
SELECT COUNT(NAME)
FROM tbl_teacher
WHERE NAME LIKE '%封%'
#试题四、查询没有学过小甄老师课的同学的学号、姓名
SELECT a.student_id ,a.name
from tbl_student a
where a.student_id not in
(select student_id from tbl_score where course_id=
(SELECT course_id from tbl_course where teacher_id=
(select teacher_id from tbl_teacher where name = '小甄')))
#试题五、查询学过"4"且学过编号"5"课程的同学的学号
SELECT a.student_id
from (select * from tbl_score where course_id = 4) a
INNER JOIN
(SELECT * from tbl_score where course_id = 5) b
on a.student_id = b.student_id
#试题六、查询课程编号"1"成绩比编号"2"成绩低的学生的学号
SELECT t1.student_id
from (select student_id,course_id,number from tbl_score where course_id =1) t1
INNER JOIN
(select student_id ,course_id,number from tbl_score where course_id =2) t2
on t1.student_id = t2.student_id
where t1.number < t2.number
order by t1.student_id
#试题七、找出有一门课程低于60分的学生的学号和名字
select b.student_id,b.`name`
from tbl_score a,tbl_student b
where a.number<60 and a.student_id =b.student_id
GROUP BY b.student_id
select t1.student_id ,t1.name
from tbl_student t1
INNER JOIN
(select student_id,MIN(number) from tbl_score
GROUP BY student_id
HAVING MIN(number)<60
) t2
on t1.student_id = t2.student_id
#试题八、查询选完全部课程的学生的学号
select a.student_id
from tbl_score a,tbl_course b
where a.course_id=b.course_id
GROUP BY a.student_id
HAVING COUNT(a.course_id)=(select COUNT(*) from tbl_course)
SELECT t1.student_id , count(t2.course_id) as totalCourse
from tbl_score t1
INNER JOIN
tbl_course t2
on t1.course_id = t2.course_id
GROUP BY t1.student_id
HAVING totalCourse = (select COUNT(course_id) from tbl_course)
#试题九、按平均成绩从高到低，显示所有学生的各科课程成绩
SELECT *
from tbl_student a,tbl_score b
where a.student_id =b.student_id
and a.student_id in(
SELECT a.student_id
FROM tbl_student a,tbl_score b
WHERE a.student_id=b.`student_id`
GROUP BY a.student_id
ORDER BY AVG(b.number) desc
)
select t.student_id , t.course_id,t.number,b.avgScore
from tbl_score t
LEFT JOIN (select student_id,AVG(number) as avgScore from tbl_score GROUP BY student_id) b
on t.student_id = b.student_id
ORDER BY avgScore desc
#试题十、查询各科成绩的最高分和最低分及对应的学生姓名学号。
SELECT c.name,c.student_id,a.number
from tbl_score a,
(
(
SELECT MAX(number) as num ,a.course_id as course_id
from tbl_course a,tbl_score b
where a.course_id=b.course_id
GROUP BY a.course_id
)
UNION
(
SELECT MIN(number) as num ,a.course_id as course_id
from tbl_course a,tbl_score b
where a.course_id=b.course_id
GROUP BY a.course_id
)
) b,tbl_student c
where a.course_id=b.course_id and a.number=b.num
and a.student_id=c.student_id
select *
from
(select a.course_id , a.student_id,b.max_number
from tbl_score a
INNER JOIN(select course_id , MAX(number) max_number from tbl_score GROUP BY course_id ) b
on a.course_id = b.course_id
where a.number = b.max_number) x1
INNER JOIN
(select c.course_id,c.student_id,d.min_number
from tbl_score c
INNER JOIN (select course_id,MIN(number) min_number from tbl_score GROUP BY course_id) d
on c.course_id =d.course_id
where c.number = d.min_number) x2
on x1.course_id = x2.course_id
ORDER BY x1.course_id