首先创建表，并在表中插入数据
--创建学生表
create table students (
id int unsigned not null auto_increment primary key,
name varchar(20) default \'\',
age tinyint unsigned default 0,
high decimal(5,2),
gender enum(\'男\', \'女\', \'中性\', \'保密\') default \'保密\',
cls_id int unsigned default 0,
is_delete bit default 0
);
--创建班级表
create table classes(
id int unsigned auto_increment primary key not null,
name varchar(20) not null
);
--往students表里插入数据
insert into students values
(0,\'小明\',18,180.00,2,1,0),
(0,\'小月月\',19,180.00,2,2,0),
(0,\'彭于晏\',28,185.00,1,1,0),
(0,\'刘德华\',58,175.00,1,2,0),
(0,\'黄蓉\',108,160.00,2,1,0),
(0,\'凤姐\',44,150.00,4,2,1),
(0,\'王祖贤\',52,170.00,2,1,1),
(0,\'周杰伦儿\',34,null,1,1,0),
(0,\'程坤\',44,181.00,1,2,0),
(0,\'和珅\',55,166.00,2,2,0),
(0,\'刘亦菲\',29,162.00,3,3,0),
(0,\'金星\',45,180.00,2,4,0),
(0,\'静香\',18,170.00,1,4,0),
(0,\'郭静\',22,167.00,2,5,0),
(0,\'周杰\',33,178.00,1,1,0),
(0,\'钱小豪\',56,178.00,1,1,0),
(0,\'谢霆锋\',38,175.00,1,1,0);
--向classes表里插入数据
insert into classes values (0, \'云唯_01期\'),(0, \'云唯_02期\');
对上面的数据进行查询实验:
inner join
内关联，连接查询：多个表连接起来查询，查询结果多个表的交集
-- 连接查询
-- inner join ... on
-- 两个表连接查询
select * from students inner join classes
-- 查询能够对应班级的学生以及班级信息
select * from students inner join classes on students.cls_id=classes.id;
-- 按照要求显示姓名，班级
select students.*, classes.name from students inner join classes on students.cls_id=classes.id;
--给数据表起别名
select s.name, c.name from students as s inner join classes as c on s.cls_id=c.id;
-- 在以上查询中将班级姓名显示在第一列
select classes.name,students.* from students inner join classes on students.cls_id=classes.id;
-- 查询有能够对应班级的学生以及班级信息，按照班级进行排序
select classes.id, students.* from students inner join classes on students.cls_id=classes.id order by classes.id;
-- 当是同一个班级的时候，按照学生的id从小到大
select classes.id, students.* from students inner join classes on students.cls_id=classes.id order by classes.id, students.id;
-- 自关联
create table areas(
aid int primary key auto_increment,
name varchar(20),
pid int
);
-- 查询出河北省所有市
--需要起别名
select * from areas as province inner join areas as city on province.aid=city.pid having name=\'河北省\';
select province.name,city.name from areas as province inner join areas as city on province.aid=city.pid having province.name=\'河北省\';
-- 子查询
-- 标量子查询
-- 查询出北京市所有区的信息
select * from areas where pid=(select aid from areas where name=\'北京市\');
select * from areas where pid in (select aid from areas where name=\'北京市\');