联合查询

select * from my_class

union -- 默认去重

select * from my_class;

select * from my_class

union all -- 不去重

select * from my_class;

select id,c_name,room from my_class

union all -- 不去重

select name,number,idfrom my_student;

-- 需求：男生升序，女生降序（年龄）(

select * from my_studentwhere sex='男' order by age asc limit 9999999)

union(

select *from my_studentwhere sex='女' order by agedesc limit 9999999);

 标量子查询

select * from my_studentwhere c_id=(select id from my_classwhere name='python1910');

 列子查询

select * from my_studentwhere c_idin (select id from my_class);

-- any some all

select * from my_studentwhere c_id =any (select id from my_class);

select * from my_studentwhere c_id =some (select id from my_class);

select * from my_studentwhere c_id =all (select id from my_class);

select * from my_studentwhere c_id !=any (select id from my_class);-- 所有结果（null除外）

select * from my_studentwhere c_id !=some (select id from my_class);-- 所有结果（null除外）

select * from my_studentwhere c_id !=all (select id from my_class);-- 1,2不等于345（null除外）

select * from my_studentwhere age=(select max(age)from my_student)and height=(select max(height)from my_student);

行子查询

select * from my_studentwhere (age,height)= (select max(age),max(height)from my_student);

select *from my_studentorder by age desc,heightdesc limit 1;-- 可能查询结果不是预想的

 表子查询

select * from my_studentgroup by c_idorder by heightdesc;

-- 插入学生

insert into my_studentvalues (null,'bc20200007','小红','女',25,185,1);

-- 查找每个班身高最高的学生

select * from (select * from my_studentorder by heightdesc limit 9999999)as studentgroup by c_id;

--

select exists(select * from my_student);

select exists(select * from my_studentwhere id=100);

exists子查询

select * from my_studentwhere  exists(select * from my_class);-- 判断括号里是否成立

select * from my_studentwhere  exists(select * from my_classwhere id=3);

select * from my_studentwhere  exists(select * from my_classwhere id=2);