MySQl基本查询语句练习
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六、select语句练习
简单语句查询
1. select * from students; ------显示表中的所有内容
2. select Name,Age from students; ------显示students表中的Name和Age 列
3. select distict Gender from students; ------相同的内容只显示一次
选择students表中年龄大于20的同学(以下三种方式):
4. select * from students where Age>=20;
5. select Name,Age from students where Age>=20;
6. select Name,Age from students where Age+1>20;
查找年龄大于20的同学并且按降序排列:
7. select Name,Age from students where Age>20 order by Age desc;
年龄大于等于20并且是男性的同学:
8. select Name from students where Age>20 and Gender='M';
年龄不大于20的同学:
9. select Name,Age,Gender from students where not Age>20;
小于等于20的女同学:
10. select Name,Age,Gender from students where not (Age>20 or Gen der=…M‟);
年龄在(21-24)之间的同学(以下两种方式):
11. select Name,Age from students where Age>20 and Age<25;
12. select Name,Age from students where Age between 20 and 25;
显示以Y开头的名称(这里限定了姓名的长度)("_"表示任意单个字符):
13. select Name from students where Name like 'Y___';
显示以Y开头的姓名:
14. select Name from students where Name like 'Y%';
名称中含有ing的名称(“%”表示任意长度的任意字符):
15. select Name from students where Name like '%ing%';
显示以M或N或Y开头的名字(支持正则表达式):
16. select Name from students where Name rlike '^[MNY].*$';
显示年龄是18、20、25的同学:
17. select Name from students where Age IN (18,20,25);
显示挑选课程号(CID1)为空的同学:
18. select Name from students where CID1 is null;
把查询后的结果进行降序排序(ASC升序,desc降序)
19. select Name,CID1 from students where CID1 is not null order b y CID1 desc;
显示查询的Name表头名变为name
20. select Name AS Student_Name from students;
隔两行数据向后取三行数据:
21. select Name from students limit 2,3;
所有同学的平均年龄:
22. select AVG(age) from students;
显示年龄最大的同学:
23. select MAX(age) from students;
显示年龄最小的同学:
24. select MIN(age) from students;
显示所有同学的年龄总和:
25. select SUM(age) from students;
显示所有同学的个数:
26. select count(age) from students;
显示所有男同学的平均年龄:
27. select AVG(age) from students where Gender=‟M…;
显示所有女同学的平均年龄:
28. select AVG(age) from students where Gender=‟F…;
显示男女同学的平均年龄:
29. select Gender,avg(age) from students group by Gender;
显示选修CID1的同学
30. select count(CID1) AS Persons,CID1 from students group by CI D1;
显示选修人数大于2的课程:
31. select count(CID1) AS Persons,CID1 from students group by CI D1 having Persons>=2;
七、多表查询
每位同学及其他所学习的课程名称(以下四种方式)
1. select ,ame from students,
courses where students.CID1=courses.CID;
2. select ,ame from students,
courses where students.CID1=courses.CID;
3. select ,ame from students AS s left jion courses AS
c on s.CID1=c.CID;(左连接)
4. select ,ame from students AS s right jion courses AS
c on s.CID1=c.CID;(右连接)
显示各个同学与他相对应的导师:
5. select as student, as teacher from students as s, students as c where s.SID=c.TID;
显示每一位老师及其所教授的课程;没有教授的课程保持为NULL:
6. select t.Tname,ame from tutors as t left join courses as c on t.TID=c.TID;
显示每一个课程及其相关的老师,没有老师教授的课程将其老师显示为空:
7. select t.Tname,ame from tutors as t right jion courses as
c on t.TID=c.TID;
显示每位同学CID1课程的课程名及其讲授了相关课程的老师的名称:
8. select Name,Cname,Tname from students,courses,tutors where stu dents.CID1=courses.CID and courses.TID=tutors.TID;
查看同学的成绩及姓名,并且按升序排列: