Mysql练习题

1.自行创建测试数据

2.查询学生总人数

3.查询生物课和物理课都及格的学生id和姓名

首先，查询生物课和物理课及格的同学（三表查询）：

生物课及格(三表查询)：
select student.student_id,sname from student 
inner join score
on student.student_id = score.student_id
inner join course
on course.course_id = score.course_id  
where cname = '生物' and score>60

物理课及格(三表查询)： 
select student.student_id,sname from student 
inner join score 
on student.student_id = score.student_id 
inner join course 
on course.course_id = score.course_id 
where cname = '物理' and score>60

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其次，求两个结果的并集（Mysql中与SQL Server、Oracle不同，不支持Intersect语句，因此mysql求并集需要用到INNER JOIN xxx USING xxx语句）

select distinct student.student_id,student.sname from student
inner join
(select student.student_id,student.sname from student 
inner join score
on student.student_id = score.student_id
inner join course
on course.course_id = score.course_id  
where cname = '物理' and score>60) t0 using (student_id)
inner join 
(select student.student_id,student.sname from student 
inner join score
on student.student_id = score.student_id
inner join course
on course.course_id = score.course_id  
where cname = '生物' and score>60) t1 using (student_id);

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PS:INNER JOIN xxx USING xxx语句的使用举例：

SELECT DISTINCT RESOURCE_ID FROM USER_DEFINED_VALUE   
INNER JOIN (SELECT DISTINCT RESOURCE_ID FROM USER_DEFINED_VALUE WHERE  (COLUMN_NAME = 'A' AND VALUE in ('1')) ) t0 USING (RESOURCE_ID)   
INNER JOIN (SELECT DISTINCT RESOURCE_ID FROM USER_DEFINED_VALUE WHERE  (COLUMN_NAME = 'B' AND VALUE in ('2')) ) t1 USING (RESOURCE_ID)  

第一句话会查出表中所有的资源ID
第二句话或查出属性A='1'的资源ID，并和第一句话的查询结果取交集
第三句话或查出属性B='2'的资源ID，并和前面的查询结果取交集
using等价于join操作中的on
这样，还可以继续加其他的属性

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