10分钟学会MySQL

10分钟学会MySQL，其实只是个标题。10分钟肯定不能让大家从小白变成高手，但入门足够了。

因为最近公司招聘遇到了一个做了4年PHP开发，薪资要求1.2k/月。本身是没打算面试mysql这些题目的，毕竟太基础，不合适。所以先问了下缓存架构算法之类的。结果一问三不知。所以最后问题就变成了两个。一个是用PHP给[1,3,5,2,4,6,10,9,8]排个顺序，从小到大或从大到小均可。另外一道题就是有两个数据库表，需要查出picture字段不为空时的数据。

面试结果真是让人很无语。所以今天分享一篇博客。把MySQL常用的查询语句为大家列一下，基础不好或刚刚入门的朋友可以收藏下。

#### SELECT 常用语句####
#查询年龄在18-19的学生
#select * from student where Sage between 18 and 19;
#查询年龄不在18-19的学生
#select * from student where Sage not between 18 and 19;
#查询计算机科学系(CS系)，数学系(MA系)和信息系(IS)学生
#select * from student where Sdept in('CS','MA','IS');
#查询既不是计算机系(IS系)，也不是信息系(MA系)和信息系(IS系)学生
#select * from student where Sdept not in('CS','MA','IS');
#查询姓刘的学生
#select * from student where Sname like '刘%';
#查询姓欧阳，且全名为三个汉字的学生
#select *from student where Sname like '欧阳_';
#查询名字中第二个字为晨的学生
#select * from student where Sname like '_晨';
#查询不姓刘的学生
#select * from student where Sname not like '刘%';
#查询缺少成绩的学生的学号和相对的课程号
#select sno,cno from sc where grade is null;
#查询所有有成绩的学生的学号和课程号
#select sno,cno from sc where grade is not null;
#查询选修了3号课程的学生的学号，姓名和分数，按成绩降序排序
#select sc.sno,student.sname,sc.grade from student,sc where cno=3 and student.sno=sc.sno order by grade desc;
#查询全体学生，按所在系升序排序，同一个系按年龄降序
#select * from student order by sdept asc,sage desc ;
#查询学生总人数
#select count(*) from student;
#查询选修了课程的学生总人数
#select count(distinct sno) from sc ;
#计算3号课程的平均分
#select avg(grade) from sc where cno=2;
#查询学号201215121 选修课程的总分数
#select sum(grade) from sc where sno='201215121';
#查询每个学生及其选修课的情况
#select * from student, sc where student.sno = sc.sno;
#查询选修了2号课程且成绩在90分以上的所有学生
#select * from sc where cno=2 and grade>90;
#左外连接
#select student.Sno,Sname,Ssex,Sage,Sdept,Cno,Grade from student left outer join sc on (student.sno = sc.sno);
#多表连接
#select student.sno,sname,cname,grade from student, sc, course where student.sno = sc.sno and course.cno = sc.cno
#嵌套查询-查询选修了2号课程的学习姓名
#select sname from student where sno in (select sno from sc where cno='2');
#查询与刘晨在同一系学习的学生
#select * from student where sdept = (select sdept from student where sname = '刘晨');
#select * from student where sdept in (select sdept from student where sname = '刘晨');
#select * from student s1,student s2 where s1.sdept = s2.sdept and s1.sname = '刘晨';
#查询选修了信息系统的学生
#select * from student,sc,course where sc.sno = student.sno and sc.cno = course.cno and course.cname = '信息系统'; ;
#select * from student where sno in (select sno from sc where cno = ( select cno from course where cname = '信息系统' ));
#找出每个学生超过其选修平均成绩的课程号
#select * from sc where grade > (select avg(grade) from sc where sno = sc.Sno);
#查询非计算机科学系中比计算机科学系任意一个学生年龄小的学生
#select * from student where sage < any (select sage from student) and sdept != 'cs';
#select * from student where sage < (select max(sage) from student) and sdept != 'cs';
#查询非计算机系中比计算机系所有年龄都要小的学生
#select * from student where sage < all (select sage from student ) and sdept != 'cs';
#select * from student where sage < (select min(sage) from student);
#查询选修了2号课程的学生
#select * from student where exists (select * from sc where cno = 2 and sc.sno = student.sno);
#select * from student where sno in (select sno from sc where cno = 2);
#查询没有选修2号课程的学生
#select * from student where not exists (select * from sc where cno = 2 and sc.sno = student.sno);
#select * from student where student.sno not in (select sc.sno from sc where sc.sno = 2);
#查询选修了全部课程的学生
-- select * from student where not exists
-- (
-- select * from course where not exists
-- (
-- select * from sc where sc.sno = student.sno and cno = course.cno
-- )
-- )
-- select sno from
-- (
-- select sno,count(*) as sum from sc group by sno having sum =
-- (
-- select count(*) from course
-- )
-- ) as A
# 集合查询 UNION (或，并集)
#select * from student where Sname = '罗琪' UNION select * from student where Sname = '刘言曌';
#select * from student where Sname = '罗琪' or Sname = '刘言曌';
#找出每个学生超过自己选修课程平均成绩的课程号
-- select * from sc,
-- (
-- select sno,avg(grade) as avg_grade from sc group by sno
-- ) as A
-- where A.sno = sc.sno and sc.grade > A.avg_grade;
#### INSERT 常用语句 ####
#将一个新学生插入到 Student 表中
#insert into Student value(201215128, '曹志雄', '男', 20, 'MA');
#insert into student(sno,sname,ssex,sage,sdept) values (201215207, '曹阿瞒','男',19, 'IS');
#### UPDATE 常用语句 ####
#修改某一个元组的值
#将罗琪的年龄-1
#update student set Sage = '18' where Sname = '罗琪'
#修改多个元组的值
#将所有的学生年龄-1
#update Student set Sage = Sage - 1;
#带子查询的修改语句
#将计算机系的学生成绩+5
-- update sc
-- set grade = grade + 5
-- where sno in
-- (select sno from student where sdept = 'CS');
#### DELETE 常用语句 ####
#先添加一条学生记录，然后删除他
#insert into student value(201215130,'张三','男',19,'IS');
#delete from student where sno = '201215130';
#删除多条记录
##delete from sc;
#### 空值的处理 ####
#空值产生
#添加一个学生，学院为NULL
#insert into student value(201215208, '春日风','女',18,NULL);
#将曹志雄的学院设置为NULL
#update student set sdept = NULL where sname = '曹志雄';
#空值判断
#查询没有先行课的课程
#select * from course where cpno is null;
#查询有先行课的课程
#select * from course where cpno is not null
#### 视图常用语句 ####
#创建一个男生视图
-- create view is_boy
-- as
-- select * from student where ssex = '男';
#查询视图
#select * from is_boy where sage < 19
#更新视图
#update is_boy set sage = sage +1 where sname = '刘中江'
#删除视图
#drop view is_boy;