查询课程‘3-105’成绩比课程‘3-245’的任意一条成绩高的成绩记录
其实这个题用min也可以做,但是这里重点学习任意一个。
任意一个:any
所以就是:
select cno,sno,degree from score where cno=‘3-105’
and degree >
any(select degree from score where cno=‘3-245’)
order by degree desc;
查询结果:
mysql> select cno,sno,degree from score
-> where cno='3-105'
-> and degree >
-> any(select degree from score where cno='3-245')
-> order by degree desc;
+-------+-----+--------+
| cno | sno | degree |
+-------+-----+--------+
| 3-105 | 103 | 92 |
| 3-105 | 102 | 91 |
| 3-105 | 101 | 90 |
| 3-105 | 104 | 89 |
| 3-105 | 105 | 88 |
| 3-105 | 109 | 76 |
+-------+-----+--------+
查询课程‘3-105’成绩比课程‘3-245’的所有成绩高的成绩记录
其实和上一题很想,这个题用max也可以写的
我们只需要把查询出来的‘3-245’的成绩筛选条件改为所有
也就是all(select degree from score where cno=‘3-245’)
全部的语句:
select cno,sno,degree from score
where cno=‘3-105’
and degree >
all(select degree from score where cno=‘3-245’);
查询结果:
mysql> select cno,sno,degree from score
-> where cno='3-105'
-> and degree >
-> all(select degree from score where cno='3-245');
+-------+-----+--------+
| cno | sno | degree |
+-------+-----+--------+
| 3-105 | 101 | 90 |
| 3-105 | 102 | 91 |
| 3-105 | 103 | 92 |
| 3-105 | 104 | 89 |
| 3-105 | 105 | 88 |
+-------+-----+--------+
查询所有教师和学生的名字,性别和生日
首先我们可以在教师表中查询所有老师的名字性别和生日:
ysql> select tname,tsex,tbirthday from teacher;
+-------+------+---------------------+
| tname | tsex | tbirthday |
+-------+------+---------------------+
| 李诚 | 男 | 1958-12-02 00:00:00 |
| 王萍 | 女 | 1972-05-05 00:00:00 |
| 刘冰 | 女 | 1977-08-14 00:00:00 |
| 张旭 | 男 | 1969-03-12 00:00:00 |
+-------+------+---------------------+
然后我们可以再学生表中查询所有学生的名字,性别和生日:
mysql> select sname,ssex,sbirthday from students;
+--------+------+---------------------+
| sname | ssex | sbirthday |
+--------+------+---------------------+
| 曾华 | 男 | 1977-09-01 00:00:00 |
| 匡明 | 男 | 1975-10-02 00:00:00 |
| 王丽 | 女 | 1976-01-23 00:00:00 |
| 李军 | 男 | 1975-02-10 00:00:00 |
| 王芳 | 女 | 1974-06-03 00:00:00 |
| 陆君 | 男 | 1974-06-03 00:00:00 |
| 王尼玛 | 男 | 1976-02-20 00:00:00 |
| 张全蛋 | 男 | 1975-02-10 00:00:00 |
| 赵铁柱 | 男 | 1974-06-03 00:00:00 |
+--------+------+---------------------+
现在我们有了学生和教师两张表,我们要怎么把这两张表连接起来呢?
如果要连接两个查询结果,需要用到union关键字:
select tname,tsex,tbirthday from teacher
union
select sname,ssex,sbirthday from students;
看一下结果:
mysql> select tname,tsex,tbirthday from teacher
-> union
-> select sname,ssex,sbirthday from students;
+--------+------+---------------------+
| tname | tsex | tbirthday |
+--------+------+---------------------+
| 李诚 | 男 | 1958-12-02 00:00:00 |
| 王萍 | 女 | 1972-05-05 00:00:00 |
| 刘冰 | 女 | 1977-08-14 00:00:00 |
| 张旭 | 男 | 1969-03-12 00:00:00 |
| 曾华 | 男 | 1977-09-01 00:00:00 |
| 匡明 | 男 | 1975-10-02 00:00:00 |
| 王丽 | 女 | 1976-01-23 00:00:00 |
| 李军 | 男 | 1975-02-10 00:00:00 |
| 王芳 | 女 | 1974-06-03 00:00:00 |
| 陆君 | 男 | 1974-06-03 00:00:00 |
| 王尼玛 | 男 | 1976-02-20 00:00:00 |
| 张全蛋 | 男 | 1975-02-10 00:00:00 |
| 赵铁柱 | 男 | 1974-06-03 00:00:00 |
+--------+------+---------------------+
但是我们可以看到,在每一列的第一行也就是字段名的地方写的是tname,tsex,tbirthday但是我们的表中还有学生啊,这个时候我们把要显示的字段名字给取一个别名,用as关键字:
select tname as name,tsex as sex,tbirthday as birthday from teacher
union
select sname,ssex,sbirthday from students;
第二个查询就不需要再写了,看一下查询结果:
mysql> select tname as name,tsex as sex,tbirthday as birthday from teacher
-> union
-> select sname,ssex,sbirthday from students;
+--------+-----+---------------------+
| name | sex | birthday |
+--------+-----+---------------------+
| 李诚 | 男 | 1958-12-02 00:00:00 |
| 王萍 | 女 | 1972-05-05 00:00:00 |
| 刘冰 | 女 | 1977-08-14 00:00:00 |
| 张旭 | 男 | 1969-03-12 00:00:00 |
| 曾华 | 男 | 1977-09-01 00:00:00 |
| 匡明 | 男 | 1975-10-02 00:00:00 |
| 王丽 | 女 | 1976-01-23 00:00:00 |
| 李军 | 男 | 1975-02-10 00:00:00 |
| 王芳 | 女 | 1974-06-03 00:00:00 |
| 陆君 | 男 | 1974-06-03 00:00:00 |
| 王尼玛 | 男 | 1976-02-20 00:00:00 |
| 张全蛋 | 男 | 1975-02-10 00:00:00 |
| 赵铁柱 | 男 | 1974-06-03 00:00:00 |
+--------+-----+---------------------+
查询每门课程中比该课程平均分低的成绩记录
那我们先查询一下课程表看一下:
mysql> select * from score;
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 101 | 3-105 | 90 |
| 102 | 3-105 | 91 |
| 103 | 3-105 | 92 |
| 103 | 3-245 | 86 |
| 103 | 6-166 | 85 |
| 104 | 3-105 | 89 |
| 105 | 3-105 | 88 |
| 105 | 3-245 | 75 |
| 105 | 6-166 | 79 |
| 109 | 3-105 | 76 |
| 109 | 3-245 | 68 |
| 109 | 6-166 | 81 |
+-----+-------+--------+
如我我们把这个表复制一下,我们分别叫这两个表为A表和B表:
A表 B表
+-----+-------+--------+ +-----+-------+--------+
| sno | cno | degree | | sno | cno | degree |
+-----+-------+--------+ +-----+-------+--------+
| 101 | 3-105 | 90 | | 101 | 3-105 | 90 |
| 102 | 3-105 | 91 | | 102 | 3-105 | 91 |
| 103 | 3-105 | 92 | | 103 | 3-105 | 92 |
| 103 | 3-245 | 86 | | 103 | 3-245 | 86 |
| 103 | 6-166 | 85 | | 103 | 6-166 | 85 |
| 104 | 3-105 | 89 | | 104 | 3-105 | 89 |
| 105 | 3-105 | 88 | | 105 | 3-105 | 88 |
| 105 | 3-245 | 75 | | 105 | 3-245 | 75 |
| 105 | 6-166 | 79 | | 105 | 6-166 | 79 |
| 109 | 3-105 | 76 | | 109 | 3-105 | 76 |
| 109 | 3-245 | 68 | | 109 | 3-245 | 68 |
| 109 | 6-166 | 81 | | 109 | 6-166 | 81 |
+-----+-------+--------+ +-----+-------+--------+
那么我们拿‘第一条记录| 101 | 3-105 | 90 |为例:
我们只需要算出B表中‘3-105’的平均分,看看第一条记录的degree是不是低于这个平均分的就可以了。
那么其他的记录呢?
我们做一下推广就是,拿A表的记录x,然后在B表中计算和记录x相同课程的课程平均分和记录x中的degree相比较就可以了,那接下来就是写sql语句了:
select * from score A where degree < (select avg(degree) from score B where A.cno=B.cno);
可能比较难理解这个写法,要稍微多看两遍。
看一下查询结果:
mysql> select * from score A where degree < (select avg(degree) from score B where A.cno=B.cno);
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 105 | 3-245 | 75 |
| 105 | 6-166 | 79 |
| 109 | 3-105 | 76 |
| 109 | 3-245 | 68 |
| 109 | 6-166 | 81 |
+-----+-------+--------+