MySQL传智播客--Lession25-Lession30笔记
2016-07-07 16:42
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=======================lession25=子查询(1)=============================
子查询：
场景：
查询代课天数最多的那个老师的信息。
Select t_name ,gender from teacher_class order by days desc limit 1;
逻辑没有问题：
但是出现了代课天数一致的最多的如何处理？不能是否有重复的，或者几个重复的。
换个思路：
先获得最多的代课天数是多少天，
Select max(days) from teacher_class;
再判断哪个老师的代课天数，和最大值是一样的。
mysql允许将上面的查询结果，作为一个值来使用。
Var1 = select max(days) from teacher_class;保存起来
Select t_name,gender from teacher_class where days=var1;
但是Mysql允许
Select t_name,gender from teacher_class where days=(select max(days) from teacher_class);
mysql> select t_name,gender from teacher_class where days=(select max(days) from teacher_class);
+----------+--------+
| t_name | gender |
+----------+--------+
| 韩ä | male |
| æŽç | male |
+----------+--------+
2 rows in set (0.04 sec)
定义：
语句内部的查询语句，就是子查询语句。子查询语句需要使用括号括起来。
子查询分类：
不同的分类，会有不同的使用方式。
分类标准：
(1)子查询出现的位置
(2)子查询的返回形式
返回值分类：
单一值：
一列，
多列，
表（多行，多列）
出现位置：
where型，where后，
from型，from后，
exists型
如何使用：
标量的：
获得一个值之后，使用关系运算符，进行判断。(= ,>, <, >=, <= ,!=)
列子查询：强调是一列
获得一列：通常是，多个行的一列值。
案例：
获得所有带过0228班，讲师的信息。
所有0228讲师的姓名，再利用这行姓名，查询其所有班记录。
select t_name from teacher_class where c_name = 'php0228';
mysql> select t_name from teacher_class where c_name = 'php0228';
+--------+
| t_name |
+--------+
| 韩信 |
| 李白 |
+--------+
Select t_name,c_name,days from teacher_class where t_name in (select t_name from teacher_class where c_name = 'php0228');
mysql> select t_name,c_name,days from teacher_class where t_name in (select t_name from teacher_class where c_name = 'php0228');
+--------+---------+------+
| t_name | c_name | days |
+--------+---------+------+
| 韩信 | php0115 | 21 |
| 韩信 | php0228 | 18 |
| 韩信 | php0331 | 22 |
| 李白 | php0115 | 20 |
| 李白 | php0228 | 22 |
| 韩信 | php0331 | 15 |
+--------+---------+------+
一定是使用集合类的操作符来完成：in | not in
还有其他的集合操作符：
Any（任何一个）=any(集合) 等于集合中的任何一个即可。等同于in。（功能比in要强大一些）
mysql> select t_name,c_name,days from teacher_class where t_name =any (select t_name from teacher_class where c_name = 'php0228');
+--------+---------+------+
| t_name | c_name | days |
+--------+---------+------+
| 韩信 | php0115 | 21 |
| 韩信 | php0228 | 18 |
| 韩信 | php0331 | 22 |
| 李白 | php0115 | 20 |
| 李白 | php0228 | 22 |
| 韩信 | php0331 | 15 |
+--------+---------+------+
那如果!=any(集合呢)，只要与集合中的一个元素，不相等即可。（只要这个集合里面有两个以上的行，那么这个语法基本不能起作用）
mysql> select t_name,c_name,days from teacher_class where t_name !=any (select t_name from teacher_class where c_name = 'php0228');
+-----------+---------+------+
| t_name | c_name | days |
+-----------+---------+------+
| 韩信 | php0115 | 21 |
| 韩信 | php0228 | 18 |
| 韩信 | php0331 | 22 |
| 李白 | php0115 | 20 |
| 李白 | php0228 | 22 |
| 韩非子 | php0115 | 15 |
| 韩信 | php0331 | 15 |
+-----------+---------+------+
All(集合)集合中的所有元素。
!=All(集合)不等与集合中的所有元素。等同于not in
mysql> select t_name,c_name,days from teacher_class where t_name !=all (select t_name from teacher_class where c_name = 'php0228');
+-----------+---------+------+
| t_name | c_name | days |
+-----------+---------+------+
| 韩非子 | php0115 | 15 |
| 韩非子 | php0331 | 15 |
+-----------+---------+------+
Some(集合)集合中的一些。
总结：
=any <==> in
!=all <==> not in
Some 和any同义词
All,any和some可以使用除了=,!=之外的运算符
Update teacher_class set t_name='zhanshan' where id='1';
=======================lession26=子查询(2)=============================
返回一行
在参与比较时，使用括号可以构建一行:(filed1,field2)
比如：
mysql> select t_name,gender,c_name from teacher_class where (gender,c_name) = (select distinct gender, c_name from teacher_class where t_name='李白' and c_name='php0115');
+-----------+--------+---------+
| t_name | gender | c_name |
+-----------+--------+---------+
| 韩信 | male | php0115 |
| 李白 | male | php0115 |
| 韩非子 | male | php0115 |
| 李白 | male | php0115 |
+-----------+--------+---------+
mysql> select gender, c_name from teacher_class where t_name='李白' and c_name='php0115';
+--------+---------+
| gender | c_name |
+--------+---------+
| male | php0115 |
| male | php0115 |
+--------+---------+
mysql> select distinct gender, c_name from teacher_class where t_name='李白' and c_name='php0115';
+--------+---------+
| gender | c_name |
+--------+---------+
| male | php0115 |
+--------+---------+
返回一个表：
Select * from (table) where cond;
Select * from (select t_name, c_name, days from teacher_class where days > 15) as temp;
mysql> select * from (select t_name, c_name, days from teacher_class where days > 15) as temp;
+--------+---------+------+
| t_name | c_name | days |
+--------+---------+------+
| 韩信 | php0115 | 21 |
| 韩信 | php0228 | 18 |
| 韩信 | php0331 | 22 |
| 李白 | php0115 | 20 |
| 李白 | php0228 | 22 |
+--------+---------+------+
mysql> select * from (select t_name, c_name, days from teacher_class where days > 15) as temp where t_name like '李%';
+--------+---------+------+
| t_name | c_name | days |
+--------+---------+------+
| 李白 | php0115 | 20 |
| 李白 | php0228 | 22 |
+--------+---------+------+
外部查询所使用的列名，是由子查询指定。
Select teacher from (select t_name as teacher, c_name , days from teacher_class where days > 15) as temp where teacher like '李%';
mysql> select teacher from (select t_name as teacher, c_name, days from teacher_class where days > 15) as temp where teacher like '李%';
+---------+
| teacher |
+---------+
| 李白 |
| 李白 |
+---------+
2 rows in set (0.00 sec)
=======================lession27=子查询(3)=============================
Exists
Exists(subquery)
判断依据：
如果子查询的，可以返回数据，则认为exists表达示，返回真。否则返回假。
mysql> select * from teacher_class where exists (select * from teacher
where teacher_class.id=t_id);
+----+--------+--------+---------+------+------+------------+-----------
-+
| id | t_name | gender | c_name | room | days | begin_date |
end_date |
+----+--------+--------+---------+------+------+------------+-----------
-+
| 1 | 韩信 | male | php0115 | 207 | 21 | 2013-01-15 | 2013-02-20 |
+----+--------+--------+---------+------+------+------------+-----------
-+
1 row in set (0.03 sec)
exists能实现的其他也可以实现的
Select * from teacher_class where id in (select t_id from teacher);
mysql> select * from teacher_class where id in (select t_id from
teacher);
//in的话要找地方存储起来，比如teacher有十万条记录，那么要找地方存起来in的数
据，而exists则不用存，因为它是一条一条检索的
+----+--------+--------+---------+------+------+------------+-----------
-+
| id | t_name | gender | c_name | room | days | begin_date |
end_date |
+----+--------+--------+---------+------+------+------------+-----------
-+
| 1 | 韩信 | male | php0115 | 207 | 21 | 2013-01-15 | 2013-02-20 |
| 3 | 韩信 | male | php0331 | 102 | 22 | 2013-03-31 | 2013-05-05 |
+----+--------+--------+---------+------+------+------------+-----------
-+
2 rows in set (0.00 sec)
解决思路是不一样的：
Exists:先获得每一条teacher_class的数据，然后获得id字段，去teacher表内查找对
应值，找到，说明符合条件。
In:先获得所有的id的可能性。再去检索teacher_class数据时，判断当前的id是否在i
d集合内。
=======================lession28=连接查询=============================
Join
每一个实体，一个表一个业务逻辑，使用多个实体的数据，多张表应该在一起使用，将
多个表的记录连接起来。
总体思路：
将所有的数据，按照某种条件，连接起来，再进行筛选处理。
连接的分类：
根据连接的条件不同，分类如下：
内连接
外连接
自然连接
Create table join_teacher(
Id int primary key auto_increment,
T_name varchar(10),
Gender enum('male', 'female', 'secret')
) engine innodb character set utf8;
Insert into join_teacher values
(1,'韩信','male'),
(2, '李白', 'female'),
(3, '韩非子', 'secret');
insert into join_teacher values (4, '孙武','male');
Create table join_class(
Id int primary key auto_increment,
C_name char(7),
Room char(3)
) engine innodb character set utf8;
Insert into join_class values
(1,'php0115','207'),
(2,'php0228','104'),
(3,'php0331','102');
insert into join_class values(4,'php0505','202');
create table join_teacher_class(
id int primary key auto_increment,
t_id int,
c_id int,
days tinyint,
begin_date date,
end_date date
) engine innodb character set utf8;
insert into join_teacher_class values
(1, 1, 1, 15, '2013-01-15', '2013-02-20'),
(2, 1, 2, 18, '2013-02-28', '2013-03-30'),
(3, 1, 3, 22, '2013-03-31', '2013-05-05'),
(4, 2, 1, 20, '2013-02-22', '2013-03-25'),
(5, 2, 2, 22, '2013-03-31', '2013-04-29'),
(6, 3, 1, 15, '2013-03-27', '2013-04-18'),
(7, 1, 1, 15, '2013-04-19', '2013-05-01'),
(8, 3, 3, 15, '2013-05-28', '2013-06-15'),
(9, 2, 1, 5, '2013-05-04', '2013-05-15');
更改列的列名：
alter table tbl_name change column old_name new_name new_列的类型;
mysql> select * from join_teacher;
+----+-----------+--------+
| Id | T_name | Gender |
+----+-----------+--------+
| 1 | 韩信 | male |
| 2 | 李白 | female |
| 3 | 韩非子 | secret |
| 4 | 孙武 | male |
+----+-----------+--------+
4 rows in set (0.00 sec)
ysql> alter table join_teacher change column Id id int;
Query OK, 4 rows affected (0.12 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> select * from join_teacher;
+----+-----------+--------+
| id | T_name | Gender |
+----+-----------+--------+
| 1 | 韩信 | male |
| 2 | 李白 | female |
| 3 | 韩非子 | secret |
| 4 | 孙武 | male |
+----+-----------+--------+
4 rows in set (0.00 sec)
内连接：
数据内部的连接，要求，连接的多个数据都必须存在才能进行连接。
不包含连接不到的数据。
tbl_left inner join tbl_right on 连接条件
select join_teacher.t_name, join_teacher_class.begin_date,
join_teacher_class.days from join_teacher inner join
join_teacher_class on join_teacher.id = join_teacher_class.t_id;
ql> select join_teacher.t_name, join_teacher_class.begin_date,
join_teacher_class.days from join_teacher inner join
join_teacher_class on join_teacher.id = join_teacher_class.t_id;
+-----------+------------+------+
| t_name | begin_date | days |
+-----------+------------+------+
| 韩信 | 2013-01-15 | 15 |
| 韩信 | 2013-02-28 | 18 |
| 韩信 | 2013-03-31 | 22 |
| 韩信 | 2013-04-19 | 15 |
| 李白 | 2013-02-22 | 20 |
| 李白 | 2013-03-31 | 22 |
| 李白 | 2013-05-04 | 5 |
| 韩非子 | 2013-03-27 | 15 |
| 韩非子 | 2013-05-28 | 15 |
+-----------+------------+------+
9 rows in set (0.10 sec)
1.连接
(1,'韩信','male',1, 1, 1, 15, '2013-01-15','2013-02-20')
2,判断条件 on
将连接结果保留。
3.继续连接，重复第一步
(1,'韩信','male',2,1,2, 18, '2013-02-28','2013-03-30'),保留
(1, '韩信', 'male',5, 2, 2, 22, '2013-03-31', '2013-04-29'),不满足
不满足，条件，连接结果不保留
外连接：
如果负责连接的一个或多个数据不真实存在，则称之为外连接
（孙武老师虽然没有连接上，但也出现在结果内）
select join_teacher.t_name, join_teacher_class.begin_date,
join_teacher_class.days from join_teacher left outer join
join_teacher_class on join_teacher.id = join_teacher_class.t_id;
ysql> select join_teacher.t_name, join_teacher_class.begin_date,
join_teacher_class.days from join_teacher left outer join
join_teacher_class on join_teacher.id = join_teacher_class.t_id;
+-----------+------------+------+
| t_name | begin_date | days |
+-----------+------------+------+
| 韩信 | 2013-01-15 | 15 |
| 韩信 | 2013-02-28 | 18 |
| 韩信 | 2013-03-31 | 22 |
| 韩信 | 2013-04-19 | 15 |
| 李白 | 2013-02-22 | 20 |
| 李白 | 2013-03-31 | 22 |
| 李白 | 2013-05-04 | 5 |
| 韩非子 | 2013-03-27 | 15 |
| 韩非子 | 2013-05-28 | 15 |
| 孙武 | NULL | NULL |
+-----------+------------+------+
10 rows in set (0.00 sec)
内链接的处理：
内链接，在连接时，是可以省略连接条件的。意味着，所有的左表的数据，都要与
右表的记录做一个连接。
共存在M*N个连接
这中连接，就称之为，交叉连接，或者笛卡尔积。
select join_teacher.t_name, join_teacher_class.begin_date,
join_teacher_class.days from join_teacher inner join join_teacher_class;
select join_teacher.t_name, join_teacher_class.begin_date,
join_teacher_class.days from join_teacher cross join join_teacher_class;
select join_teacher.t_name, join_teacher_class.begin_date,
join_teacher_class.days from join_teacher join join_teacher_class;
可以通过多表查询，不使用where,做到笛卡尔积。
select join_teacher.t_name, join_teacher_class.begin_date,
join_teacher_class.days from join_teacher ,join_teacher_class;
注意：mysql中cross join 与 inner join 相同，但在数据库的定义上，交叉
连接就是笛卡尔积。是没有条件的inner join.
mysql inner join 是默认的连接方案，可以省略inner.
有条件的内连接：
会在连接时过滤非法的连接。
where:数据过滤条件
on:数据连接条件
where写法：数据过滤，理解上，数据按照交叉连接连接完成后，再做数据过滤。
on的写法： 在连接时，就对数据进行判断。
using的写法:using要求，负责连接的两个实体之间的字段名称，一致。
建议是，在有同名字段时，使用using,而在通用条件时，使用on.在数据过滤时（不
是指的连接过滤）使用where.
select id, days, t_name from join_teacher inner join
join_teacher_class using (id);
select * from join_teacher join join_teacher_class;
注意：查询条件，与外连接通用（外连接，不能使用where作为连接条件）；
=======================lession29=外连接==============================
注意： 无论是连接条件，还是连接查询多字段列表，都没有必要一定要写表名.字段
的语法。是否写，取决于是否发生冲突，冲突需要写，不冲突，无所谓。
建议：如果可以写上，保证代码的可读性。
别名：
表别名，保证简介和清晰
sql> select t.t_name, tc.begin_date, tc.days from join_teacher as t
inner join join_teacher_class as tc where t.id=tc.t_id and tc.days > 15;
t_name | begin_date | days |
+--------+------------+------+
| 韩信 | 2013-02-28 | 18 |
| 韩信 | 2013-03-31 | 22 |
| 李白 | 2013-02-22 | 20 |
| 李白 | 2013-03-31 | 22 |
+--------+------------+------+
4 rows in set (0.00 sec)
列别名：
select t.id, tc.id, t.t_name, tc.begin_date, tc.days from join_teacher
as t inner join join_teacher_class as tc where t.id=tc.t_id and
tc.days > 15;
mysql> select t.id, tc.id, t.t_name, tc.begin_date, tc.days from
join_teacher as t inner join join_teacher_class as tc where
t.id=tc.t_id and tc.days > 15;
+----+----+--------+------------+------+
| id | id | t_name | begin_date | days |
+----+----+--------+------------+------+
| 1 | 2 | 韩信 | 2013-02-28 | 18 |
| 1 | 3 | 韩信 | 2013-03-31 | 22 |
| 2 | 4 | 李白 | 2013-02-22 | 20 |
| 2 | 5 | 李白 | 2013-03-31 | 22 |
+----+----+--------+------------+------+
4 rows in set (0.00 sec)
select t.id as t_id, tc.id as tc_id, t.t_name, tc.begin_date, tc.days
from join_teacher as t inner join join_teacher_class as tc where
t.id=tc.t_id and tc.days > 15;
mysql> select t.id as t_id, tc.id as tc_id, t.t_name, tc.begin_date,
tc.days from join_teacher as t inner join join_teacher_class as tc
where t.id=tc.t_id and tc.days > 15;
+------+-------+--------+------------+------+
| t_id | tc_id | t_name | begin_date | days |
+------+-------+--------+------------+------+
| 1 | 2 | 韩信 | 2013-02-28 | 18 |
| 1 | 3 | 韩信 | 2013-03-31 | 22 |
| 2 | 4 | 李白 | 2013-02-22 | 20 |
| 2 | 5 | 李白 | 2013-03-31 | 22 |
+------+-------+--------+------------+------+
4 rows in set (0.00 sec)
外连接：
分类：
左外连接
右外连接
全外连接 （mysql暂不支持）
左连接：
在连接时，如果出现左边表，数据连接不到右边表的情况，则左边表的数据在最终结
果内被保留。而如果出现右表数据连接不到左表的情况，右表数据被丢弃。
select t.id as t_id, tc.id as tc_id, t.t_name, tc.begin_date,
tc.days from join_teacher as t left join join_teacher_class as tc
on t.id=tc.t_id;
mysql> select t.id as t_id, tc.id as tc_id, t.t_name, tc.begin_date,
-> tc.days from join_teacher as t left join join_teacher_class as
tc
-> on t.id=tc.t_id;
+------+-------+-----------+------------+------+
| t_id | tc_id | t_name | begin_date | days |
+------+-------+-----------+------------+------+
| 1 | 1 | 韩信 | 2013-01-15 | 15 |
| 1 | 2 | 韩信 | 2013-02-28 | 18 |
| 1 | 3 | 韩信 | 2013-03-31 | 22 |
| 1 | 7 | 韩信 | 2013-04-19 | 15 |
| 2 | 4 | 李白 | 2013-02-22 | 20 |
| 2 | 5 | 李白 | 2013-03-31 | 22 |
| 2 | 9 | 李白 | 2013-05-04 | 5 |
| 3 | 6 | 韩非子 | 2013-03-27 | 15 |
| 3 | 8 | 韩非子 | 2013-05-28 | 15 |
| 4 | NULL | 孙武 | NULL | NULL |
+------+-------+-----------+------------+------+
10 rows in set (0.00 sec)
drop table if exists one;
create table one(
one_id int,
one_data char(1),
public_field int
);
insert into one values
(1,'a',10),
(2,'b',20),
(3,'c',30);
drop table if exists two;
create table two(
two_id int,
two_data char(1) not null default 't',
public_field int
);
insert into two values
(2,'B',20),
(3,'C',30),
(4,'D',40);
左连接：
select * from one left join two on one_id=two_id;
mysql> select * from one left join two on one_id=two_id;
+--------+----------+--------------+--------+----------+--------------+
| one_id | one_data | public_field | two_id | two_data | public_field |
+--------+----------+--------------+--------+----------+--------------+
| 1 | a | 10 | NULL | NULL | NULL |
| 2 | b | 20 | 2 | B | 20 |
| 3 | c | 30 | 3 | C | 30 |
+--------+----------+--------------+--------+----------+--------------+
3 rows in set (0.00 sec)
右连接：
select * from one right join two on one_id=two_id;
mysql> select * from one right join two on one_id=two_id;
+--------+----------+--------------+--------+----------+--------------+
| one_id | one_data | public_field | two_id | two_data | public_field |
+--------+----------+--------------+--------+----------+--------------+
| 2 | b | 20 | 2 | B | 20 |
| 3 | c | 30 | 3 | C | 30 |
| NULL | NULL | NULL | 4 | D | 40 |
+--------+----------+--------------+--------+----------+--------------+
3 rows in set (0.00 sec)
内链接：
select * from one inner join two on one_id=two_id;
mysql> select * from one inner join two on one_id=two_id;
+--------+----------+--------------+--------+----------+--------------+
| one_id | one_data | public_field | two_id | two_data | public_field |
+--------+----------+--------------+--------+----------+--------------+
| 2 | b | 20 | 2 | B | 20 |
| 3 | c | 30 | 3 | C | 30 |
+--------+----------+--------------+--------+----------+--------------+
2 rows in set (0.00 sec)
左连接+右连接 = 全外连接
mysql> (select * from one left join two on one_id=two_id)
-> union
-> (select * from one right join two on one_id=two_id);
+--------+----------+--------------+--------+----------+--------------+
| one_id | one_data | public_field | two_id | two_data | public_field |
+--------+----------+--------------+--------+----------+--------------+
| 1 | a | 10 | NULL | NULL | NULL |
| 2 | b | 20 | 2 | B | 20 |
| 3 | c | 30 | 3 | C | 30 |
| NULL | NULL | NULL | 4 | D | 40 |
+--------+----------+--------------+--------+----------+--------------+
4 rows in set (0.00 sec)
using会去掉重复字段，并且会放在最前一列，建议使用，因为去掉重复对人友好
select * from one left join two using (public_field);
mysql> select * from one left join two using (public_field);
+--------------+--------+----------+--------+----------+
| public_field | one_id | one_data | two_id | two_data |
+--------------+--------+----------+--------+----------+
| 10 | 1 | a | NULL | NULL |
| 20 | 2 | b | 2 | B |
| 30 | 3 | c | 3 | C |
+--------------+--------+----------+--------+----------+
3 rows in set (0.00 sec)
select * from one left join two on one.public_field=two.public_field;
mysql> select * from one left join two on
one.public_field=two.public_field;
+--------+----------+--------------+--------+----------+--------------+
| one_id | one_data | public_field | two_id | two_data | public_field |
+--------+----------+--------------+--------+----------+--------------+
| 1 | a | 10 | NULL | NULL | NULL |
| 2 | b | 20 | 2 | B | 20 |
| 3 | c | 30 | 3 | C | 30 |
+--------+----------+--------------+--------+----------+--------------+
3 rows in set (0.00 sec)
=======================lession30=自然连接==============================
自然连接：
通过mysql自己的判断完成连接过程：
不需要指定连接条件
mysql会使用多表内的，相同的字段，作为连接条件。
select * from one natural join two; 相当于
select * from one inner join two using(public_field);
mysql> select * from one natural join two;
+--------------+--------+----------+--------+----------+
| public_field | one_id | one_data | two_id | two_data |
+--------------+--------+----------+--------+----------+
| 20 | 2 | b | 2 | B |
| 30 | 3 | c | 3 | C |
+--------------+--------+----------+--------+----------+
2 rows in set (0.01 sec)
mysql> select * from one inner join two using(public_field);
+--------------+--------+----------+--------+----------+
| public_field | one_id | one_data | two_id | two_data |
+--------------+--------+----------+--------+----------+
| 20 | 2 | b | 2 | B |
| 30 | 3 | c | 3 | C |
+--------------+--------+----------+--------+----------+
2 rows in set (0.00 sec)
自然连接分成内外之分：
内，natural join
外，左外，右外 (左右是相对与join来说的)
natural letf join
natural right join
select * from one natural left join two;相当于
select * from one left join two using (public_field);
mysql> select * from one natural left join two;
+--------------+--------+----------+--------+----------+
| public_field | one_id | one_data | two_id | two_data |
+--------------+--------+----------+--------+----------+
| 10 | 1 | a | NULL | NULL |
| 20 | 2 | b | 2 | B |
| 30 | 3 | c | 3 | C |
+--------------+--------+----------+--------+----------+
3 rows in set (0.00 sec)
mysql> select * from one left join two using (public_field);
+--------------+--------+----------+--------+----------+
| public_field | one_id | one_data | two_id | two_data |
+--------------+--------+----------+--------+----------+
| 10 | 1 | a | NULL | NULL |
| 20 | 2 | b | 2 | B |
| 30 | 3 | c | 3 | C |
+--------------+--------+----------+--------+----------+
3 rows in set (0.00 sec)
select * from one natural right join two;相当于
select * from one right join two using(public_field);
mysql> select * from one natural right join two;
+--------------+--------+----------+--------+----------+
| public_field | two_id | two_data | one_id | one_data |
+--------------+--------+----------+--------+----------+
| 20 | 2 | B | 2 | b |
| 30 | 3 | C | 3 | c |
| 40 | 4 | D | NULL | NULL |
+--------------+--------+----------+--------+----------+
3 rows in set (0.00 sec)
mysql> select * from one right join two using(public_field);
+--------------+--------+----------+--------+----------+
| public_field | two_id | two_data | one_id | one_data |
+--------------+--------+----------+--------+----------+
| 20 | 2 | B | 2 | b |
| 30 | 3 | C | 3 | c |
| 40 | 4 | D | NULL | NULL |
+--------------+--------+----------+--------+----------+
3 rows in set (0.00 sec)
info_class; id, class_name.
info_student; id,student_name, class_id.
info_student_info: id, student_detail.
作业：
连接时支持多表连接：
select s.*, si.* from info_class as c left join info_student as s on
c.id = s.class_id left join info_student_info as si on s.id = si.id
where c.class_name='php0331';
作业2：许多著名公司的面试题
参考图片：
L30自然连接后的作业2.JPG
提示：
Match left join class on match.host_id=class.id left join class on
match.guest_id=class.id
mysql> drop table if exists class;
mysql> create table class(
-> id tinyint primary key auto_increment,
-> class_name char(7)
-> )character set utf8;
Query OK, 0 rows affected (0.10 sec)
mysql> insert into class values
-> (2,'php0331'),
-> (5,'php0228'),
-> (1,'php0115'),
-> (7,'php0505');
Query OK, 4 rows affected (0.05 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> select * from class;
+----+------------+
| id | class_name |
+----+------------+
| 2 | php0331 |
| 5 | php0228 |
| 1 | php0115 |
| 7 | php0505 |
+----+------------+
4 rows in set (0.12 sec)
// match应该是mysql的关键字创建的时候老出现问题
mysql> create table match( id tinyint primary key auto_increment,
host_id tinyint, guest_id tinyint, match_time date, match_result
char(7) )character set utf8;
ERROR 1064 (42000): You have an error in your SQL syntax; check the
manual that corresponds to your MySQL server version for the right
syntax to use near 'match( id tinyint primary key auto_increment,
host_id tinyint, guest_id tinyint,' at line 1
mysql> create table game(
id tinyint primary key auto_increment,
host_id tinyint,
guest_id tinyint,
match_time date,
match_result char(7) )character set utf8;
Query OK, 0 rows affected (0.01 sec)
mysql> insert into game values
(null,2,1,'2013-04-09','34:28'),
(null,2,7,'2013-03-09','35:45');
Query OK, 2 rows affected (0.02 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> select * from game;
+----+---------+----------+------------+--------------+
| id | host_id | guest_id | match_time | match_result |
+----+---------+----------+------------+--------------+
| 1 | 2 | 1 | 2013-04-09 | 34:28 |
| 2 | 2 | 1 | 2013-04-09 | 34:28 |
| 3 | 2 | 7 | 2013-03-09 | 35:45 |
+----+---------+----------+------------+--------------+
3 rows in set (0.00 sec)
l> delete from game where id = 1;
Query OK, 1 row affected (0.05 sec)
mysql> select * from game;
+----+---------+----------+------------+--------------+
| id | host_id | guest_id | match_time | match_result |
+----+---------+----------+------------+--------------+
| 2 | 2 | 1 | 2013-04-09 | 34:28 |
| 3 | 2 | 7 | 2013-03-09 | 35:45 |
+----+---------+----------+------------+--------------+
2 rows in set (0.00 sec)
mysql> select c.class_name,c2.class_name,g.match_time,g.match_result
from
-> game as g left join class as c on g.host_id=c.id
-> left join class as c2 on g.guest_id=c2.id;
+------------+------------+------------+--------------+
| class_name | class_name | match_time | match_result |
+------------+------------+------------+--------------+
| php0331 | php0115 | 2013-04-09 | 34:28 |
| php0331 | php0505 | 2013-03-09 | 35:45 |
+------------+------------+------------+--------------+
2 rows in set (0.00 sec)
mysql> select c.class_name,c2.class_name, g.match_time, g.match_result
from game as g left join class as c on g.host_id=c.id left join class
as c2 on g.guest_id=c2.id limit 1;
+------------+------------+------------+--------------+
| class_name | class_name | match_time | match_result |
+------------+------------+------------+--------------+
| php0331 | php0115 | 2013-04-09 | 34:28 |
+------------+------------+------------+--------------+
1 row in set (0.00 sec)
作业3：
参考图片：L30自然连接后的作业3.JPG
1.获得所有的顶级部门（即parent_id = 0）
2.获得教学部内所有的子部门。(法1，用subquery；法2 用(2)join)
mysql> create table dept(
-> id tinyint primary key auto_increment,
-> dept_name char(9),
-> parent_id tinyint
-> )character set utf8;
Query OK, 0 rows affected (0.00 sec)
1.获得所有顶级部门
mysql> select * from dept where parent_id=0;
+----+-----------+-----------+
| id | dept_name | parent_id |
+----+-----------+-----------+
| 1 | 行政部 | 0 |
| 2 | 教学部 | 0 |
+----+-----------+-----------+
2 rows in set (0.04 sec)
2.获得教学部内所有的子部门
法一：subquery
mysql> select * from dept where parent_id=
-> (select id from dept where dept_name='教学部');
+----+-----------+-----------+
| id | dept_name | parent_id |
+----+-----------+-----------+
| 3 | php | 2 |
| 4 | java | 2 |
| 5 | .net | 2 |
| 6 | 平面 | 2 |
+----+-----------+-----------+
4 rows in set (0.00 sec)
法二：join
mysql> select * from dept as son inner join dept as pa on
(son.parent_id=pa.id and pa.dept_name='教学部');
+----+-----------+-----------+----+-----------+-----------+
| id | dept_name | parent_id | id | dept_name | parent_id |
+----+-----------+-----------+----+-----------+-----------+
| 3 | php | 2 | 2 | 教学部 | 0 |
| 4 | java | 2 | 2 | 教学部 | 0 |
| 5 | .net | 2 | 2 | 教学部 | 0 |
| 6 | 平面 | 2 | 2 | 教学部 | 0 |
+----+-----------+-----------+----+-----------+-----------+
4 rows in set (0.02 sec)
优化：
mysql> select son.id,son.dept_name,pa.dept_name from dept as son inner
join dept as pa on (son.parent_id=pa.id and pa.dept_name='教学部');
+----+-----------+-----------+
| id | dept_name | dept_name |
+----+-----------+-----------+
| 3 | php | 教学部 |
| 4 | java | 教学部 |
| 5 | .net | 教学部 |
| 6 | 平面 | 教学部 |
+----+-----------+-----------+
在优化：（改了教学部dept_name为parent）
mysql> select son.id,son.dept_name,pa.dept_name as parent from dept as
son inner join dept as pa on (son.parent_id=pa.id and
pa.dept_name='教学部');
+----+-----------+-----------+
| id | dept_name | parent |
+----+-----------+-----------+
| 3 | php | 教学部 |
| 4 | java | 教学部 |
| 5 | .net | 教学部 |
| 6 | 平面 | 教学部 |
+----+-----------+-----------+
4 rows in set (0.00 sec)
4 rows in set (0.00 sec)
注意：如果不是inner join的话，会保留所有哦比如
mysql> select * from dept as son left join dept as pa on
-> (son.parent_id=pa.id and pa.dept_name='教学部');
+----+-----------+-----------+------+-----------+-----------+
| id | dept_name | parent_id | id | dept_name | parent_id |
+----+-----------+-----------+------+-----------+-----------+
| 1 | 行政部 | 0 | NULL | NULL | NULL |
| 2 | 教学部 | 0 | NULL | NULL | NULL |
| 3 | php | 2 | 2 | 教学部 | 0 |
| 4 | java | 2 | 2 | 教学部 | 0 |
| 5 | .net | 2 | 2 | 教学部 | 0 |
| 6 | 平面 | 2 | 2 | 教学部 | 0 |
| 7 | 咨询 | 1 | NULL | NULL | NULL |
| 8 | 财务 | 1 | NULL | NULL | NULL |
+----+-----------+-----------+------+-----------+-----------+
8 rows in set (0.00 sec)
子查询：
场景：
查询代课天数最多的那个老师的信息。
Select t_name ,gender from teacher_class order by days desc limit 1;
逻辑没有问题：
但是出现了代课天数一致的最多的如何处理？不能是否有重复的，或者几个重复的。
换个思路：
先获得最多的代课天数是多少天，
Select max(days) from teacher_class;
再判断哪个老师的代课天数，和最大值是一样的。
mysql允许将上面的查询结果，作为一个值来使用。
Var1 = select max(days) from teacher_class;保存起来
Select t_name,gender from teacher_class where days=var1;
但是Mysql允许
Select t_name,gender from teacher_class where days=(select max(days) from teacher_class);
mysql> select t_name,gender from teacher_class where days=(select max(days) from teacher_class);
+----------+--------+
| t_name | gender |
+----------+--------+
| 韩ä | male |
| æŽç | male |
+----------+--------+
2 rows in set (0.04 sec)
定义：
语句内部的查询语句，就是子查询语句。子查询语句需要使用括号括起来。
子查询分类：
不同的分类，会有不同的使用方式。
分类标准：
(1)子查询出现的位置
(2)子查询的返回形式
返回值分类：
单一值：
一列，
多列，
表（多行，多列）
出现位置：
where型，where后，
from型，from后，
exists型
如何使用：
标量的：
获得一个值之后，使用关系运算符，进行判断。(= ,>, <, >=, <= ,!=)
列子查询：强调是一列
获得一列：通常是，多个行的一列值。
案例：
获得所有带过0228班，讲师的信息。
所有0228讲师的姓名，再利用这行姓名，查询其所有班记录。
select t_name from teacher_class where c_name = 'php0228';
mysql> select t_name from teacher_class where c_name = 'php0228';
+--------+
| t_name |
+--------+
| 韩信 |
| 李白 |
+--------+
Select t_name,c_name,days from teacher_class where t_name in (select t_name from teacher_class where c_name = 'php0228');
mysql> select t_name,c_name,days from teacher_class where t_name in (select t_name from teacher_class where c_name = 'php0228');
+--------+---------+------+
| t_name | c_name | days |
+--------+---------+------+
| 韩信 | php0115 | 21 |
| 韩信 | php0228 | 18 |
| 韩信 | php0331 | 22 |
| 李白 | php0115 | 20 |
| 李白 | php0228 | 22 |
| 韩信 | php0331 | 15 |
+--------+---------+------+
一定是使用集合类的操作符来完成：in | not in
还有其他的集合操作符：
Any（任何一个）=any(集合) 等于集合中的任何一个即可。等同于in。（功能比in要强大一些）
mysql> select t_name,c_name,days from teacher_class where t_name =any (select t_name from teacher_class where c_name = 'php0228');
+--------+---------+------+
| t_name | c_name | days |
+--------+---------+------+
| 韩信 | php0115 | 21 |
| 韩信 | php0228 | 18 |
| 韩信 | php0331 | 22 |
| 李白 | php0115 | 20 |
| 李白 | php0228 | 22 |
| 韩信 | php0331 | 15 |
+--------+---------+------+
那如果!=any(集合呢)，只要与集合中的一个元素，不相等即可。（只要这个集合里面有两个以上的行，那么这个语法基本不能起作用）
mysql> select t_name,c_name,days from teacher_class where t_name !=any (select t_name from teacher_class where c_name = 'php0228');
+-----------+---------+------+
| t_name | c_name | days |
+-----------+---------+------+
| 韩信 | php0115 | 21 |
| 韩信 | php0228 | 18 |
| 韩信 | php0331 | 22 |
| 李白 | php0115 | 20 |
| 李白 | php0228 | 22 |
| 韩非子 | php0115 | 15 |
| 韩信 | php0331 | 15 |
+-----------+---------+------+
All(集合)集合中的所有元素。
!=All(集合)不等与集合中的所有元素。等同于not in
mysql> select t_name,c_name,days from teacher_class where t_name !=all (select t_name from teacher_class where c_name = 'php0228');
+-----------+---------+------+
| t_name | c_name | days |
+-----------+---------+------+
| 韩非子 | php0115 | 15 |
| 韩非子 | php0331 | 15 |
+-----------+---------+------+
Some(集合)集合中的一些。
总结：
=any <==> in
!=all <==> not in
Some 和any同义词
All,any和some可以使用除了=,!=之外的运算符
Update teacher_class set t_name='zhanshan' where id='1';
=======================lession26=子查询(2)=============================
返回一行
在参与比较时，使用括号可以构建一行:(filed1,field2)
比如：
mysql> select t_name,gender,c_name from teacher_class where (gender,c_name) = (select distinct gender, c_name from teacher_class where t_name='李白' and c_name='php0115');
+-----------+--------+---------+
| t_name | gender | c_name |
+-----------+--------+---------+
| 韩信 | male | php0115 |
| 李白 | male | php0115 |
| 韩非子 | male | php0115 |
| 李白 | male | php0115 |
+-----------+--------+---------+
mysql> select gender, c_name from teacher_class where t_name='李白' and c_name='php0115';
+--------+---------+
| gender | c_name |
+--------+---------+
| male | php0115 |
| male | php0115 |
+--------+---------+
mysql> select distinct gender, c_name from teacher_class where t_name='李白' and c_name='php0115';
+--------+---------+
| gender | c_name |
+--------+---------+
| male | php0115 |
+--------+---------+
返回一个表：
Select * from (table) where cond;
Select * from (select t_name, c_name, days from teacher_class where days > 15) as temp;
mysql> select * from (select t_name, c_name, days from teacher_class where days > 15) as temp;
+--------+---------+------+
| t_name | c_name | days |
+--------+---------+------+
| 韩信 | php0115 | 21 |
| 韩信 | php0228 | 18 |
| 韩信 | php0331 | 22 |
| 李白 | php0115 | 20 |
| 李白 | php0228 | 22 |
+--------+---------+------+
mysql> select * from (select t_name, c_name, days from teacher_class where days > 15) as temp where t_name like '李%';
+--------+---------+------+
| t_name | c_name | days |
+--------+---------+------+
| 李白 | php0115 | 20 |
| 李白 | php0228 | 22 |
+--------+---------+------+
外部查询所使用的列名，是由子查询指定。
Select teacher from (select t_name as teacher, c_name , days from teacher_class where days > 15) as temp where teacher like '李%';
mysql> select teacher from (select t_name as teacher, c_name, days from teacher_class where days > 15) as temp where teacher like '李%';
+---------+
| teacher |
+---------+
| 李白 |
| 李白 |
+---------+
2 rows in set (0.00 sec)
=======================lession27=子查询(3)=============================
Exists
Exists(subquery)
判断依据：
如果子查询的，可以返回数据，则认为exists表达示，返回真。否则返回假。
mysql> select * from teacher_class where exists (select * from teacher
where teacher_class.id=t_id);
+----+--------+--------+---------+------+------+------------+-----------
-+
| id | t_name | gender | c_name | room | days | begin_date |
end_date |
+----+--------+--------+---------+------+------+------------+-----------
-+
| 1 | 韩信 | male | php0115 | 207 | 21 | 2013-01-15 | 2013-02-20 |
+----+--------+--------+---------+------+------+------------+-----------
-+
1 row in set (0.03 sec)
exists能实现的其他也可以实现的
Select * from teacher_class where id in (select t_id from teacher);
mysql> select * from teacher_class where id in (select t_id from
teacher);
//in的话要找地方存储起来，比如teacher有十万条记录，那么要找地方存起来in的数
据，而exists则不用存，因为它是一条一条检索的
+----+--------+--------+---------+------+------+------------+-----------
-+
| id | t_name | gender | c_name | room | days | begin_date |
end_date |
+----+--------+--------+---------+------+------+------------+-----------
-+
| 1 | 韩信 | male | php0115 | 207 | 21 | 2013-01-15 | 2013-02-20 |
| 3 | 韩信 | male | php0331 | 102 | 22 | 2013-03-31 | 2013-05-05 |
+----+--------+--------+---------+------+------+------------+-----------
-+
2 rows in set (0.00 sec)
解决思路是不一样的：
Exists:先获得每一条teacher_class的数据，然后获得id字段，去teacher表内查找对
应值，找到，说明符合条件。
In:先获得所有的id的可能性。再去检索teacher_class数据时，判断当前的id是否在i
d集合内。
=======================lession28=连接查询=============================
Join
每一个实体，一个表一个业务逻辑，使用多个实体的数据，多张表应该在一起使用，将
多个表的记录连接起来。
总体思路：
将所有的数据，按照某种条件，连接起来，再进行筛选处理。
连接的分类：
根据连接的条件不同，分类如下：
内连接
外连接
自然连接
Create table join_teacher(
Id int primary key auto_increment,
T_name varchar(10),
Gender enum('male', 'female', 'secret')
) engine innodb character set utf8;
Insert into join_teacher values
(1,'韩信','male'),
(2, '李白', 'female'),
(3, '韩非子', 'secret');
insert into join_teacher values (4, '孙武','male');
Create table join_class(
Id int primary key auto_increment,
C_name char(7),
Room char(3)
) engine innodb character set utf8;
Insert into join_class values
(1,'php0115','207'),
(2,'php0228','104'),
(3,'php0331','102');
insert into join_class values(4,'php0505','202');
create table join_teacher_class(
id int primary key auto_increment,
t_id int,
c_id int,
days tinyint,
begin_date date,
end_date date
) engine innodb character set utf8;
insert into join_teacher_class values
(1, 1, 1, 15, '2013-01-15', '2013-02-20'),
(2, 1, 2, 18, '2013-02-28', '2013-03-30'),
(3, 1, 3, 22, '2013-03-31', '2013-05-05'),
(4, 2, 1, 20, '2013-02-22', '2013-03-25'),
(5, 2, 2, 22, '2013-03-31', '2013-04-29'),
(6, 3, 1, 15, '2013-03-27', '2013-04-18'),
(7, 1, 1, 15, '2013-04-19', '2013-05-01'),
(8, 3, 3, 15, '2013-05-28', '2013-06-15'),
(9, 2, 1, 5, '2013-05-04', '2013-05-15');
更改列的列名：
alter table tbl_name change column old_name new_name new_列的类型;
mysql> select * from join_teacher;
+----+-----------+--------+
| Id | T_name | Gender |
+----+-----------+--------+
| 1 | 韩信 | male |
| 2 | 李白 | female |
| 3 | 韩非子 | secret |
| 4 | 孙武 | male |
+----+-----------+--------+
4 rows in set (0.00 sec)
ysql> alter table join_teacher change column Id id int;
Query OK, 4 rows affected (0.12 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> select * from join_teacher;
+----+-----------+--------+
| id | T_name | Gender |
+----+-----------+--------+
| 1 | 韩信 | male |
| 2 | 李白 | female |
| 3 | 韩非子 | secret |
| 4 | 孙武 | male |
+----+-----------+--------+
4 rows in set (0.00 sec)
内连接：
数据内部的连接，要求，连接的多个数据都必须存在才能进行连接。
不包含连接不到的数据。
tbl_left inner join tbl_right on 连接条件
select join_teacher.t_name, join_teacher_class.begin_date,
join_teacher_class.days from join_teacher inner join
join_teacher_class on join_teacher.id = join_teacher_class.t_id;
ql> select join_teacher.t_name, join_teacher_class.begin_date,
join_teacher_class.days from join_teacher inner join
join_teacher_class on join_teacher.id = join_teacher_class.t_id;
+-----------+------------+------+
| t_name | begin_date | days |
+-----------+------------+------+
| 韩信 | 2013-01-15 | 15 |
| 韩信 | 2013-02-28 | 18 |
| 韩信 | 2013-03-31 | 22 |
| 韩信 | 2013-04-19 | 15 |
| 李白 | 2013-02-22 | 20 |
| 李白 | 2013-03-31 | 22 |
| 李白 | 2013-05-04 | 5 |
| 韩非子 | 2013-03-27 | 15 |
| 韩非子 | 2013-05-28 | 15 |
+-----------+------------+------+
9 rows in set (0.10 sec)
1.连接
(1,'韩信','male',1, 1, 1, 15, '2013-01-15','2013-02-20')
2,判断条件 on
将连接结果保留。
3.继续连接，重复第一步
(1,'韩信','male',2,1,2, 18, '2013-02-28','2013-03-30'),保留
(1, '韩信', 'male',5, 2, 2, 22, '2013-03-31', '2013-04-29'),不满足
不满足，条件，连接结果不保留
外连接：
如果负责连接的一个或多个数据不真实存在，则称之为外连接
（孙武老师虽然没有连接上，但也出现在结果内）
select join_teacher.t_name, join_teacher_class.begin_date,
join_teacher_class.days from join_teacher left outer join
join_teacher_class on join_teacher.id = join_teacher_class.t_id;
ysql> select join_teacher.t_name, join_teacher_class.begin_date,
join_teacher_class.days from join_teacher left outer join
join_teacher_class on join_teacher.id = join_teacher_class.t_id;
+-----------+------------+------+
| t_name | begin_date | days |
+-----------+------------+------+
| 韩信 | 2013-01-15 | 15 |
| 韩信 | 2013-02-28 | 18 |
| 韩信 | 2013-03-31 | 22 |
| 韩信 | 2013-04-19 | 15 |
| 李白 | 2013-02-22 | 20 |
| 李白 | 2013-03-31 | 22 |
| 李白 | 2013-05-04 | 5 |
| 韩非子 | 2013-03-27 | 15 |
| 韩非子 | 2013-05-28 | 15 |
| 孙武 | NULL | NULL |
+-----------+------------+------+
10 rows in set (0.00 sec)
内链接的处理：
内链接，在连接时，是可以省略连接条件的。意味着，所有的左表的数据，都要与
右表的记录做一个连接。
共存在M*N个连接
这中连接，就称之为，交叉连接，或者笛卡尔积。
select join_teacher.t_name, join_teacher_class.begin_date,
join_teacher_class.days from join_teacher inner join join_teacher_class;
select join_teacher.t_name, join_teacher_class.begin_date,
join_teacher_class.days from join_teacher cross join join_teacher_class;
select join_teacher.t_name, join_teacher_class.begin_date,
join_teacher_class.days from join_teacher join join_teacher_class;
可以通过多表查询，不使用where,做到笛卡尔积。
select join_teacher.t_name, join_teacher_class.begin_date,
join_teacher_class.days from join_teacher ,join_teacher_class;
注意：mysql中cross join 与 inner join 相同，但在数据库的定义上，交叉
连接就是笛卡尔积。是没有条件的inner join.
mysql inner join 是默认的连接方案，可以省略inner.
有条件的内连接：
会在连接时过滤非法的连接。
where:数据过滤条件
on:数据连接条件
where写法：数据过滤，理解上，数据按照交叉连接连接完成后，再做数据过滤。
on的写法： 在连接时，就对数据进行判断。
using的写法:using要求，负责连接的两个实体之间的字段名称，一致。
建议是，在有同名字段时，使用using,而在通用条件时，使用on.在数据过滤时（不
是指的连接过滤）使用where.
select id, days, t_name from join_teacher inner join
join_teacher_class using (id);
select * from join_teacher join join_teacher_class;
注意：查询条件，与外连接通用（外连接，不能使用where作为连接条件）；
=======================lession29=外连接==============================
注意： 无论是连接条件，还是连接查询多字段列表，都没有必要一定要写表名.字段
的语法。是否写，取决于是否发生冲突，冲突需要写，不冲突，无所谓。
建议：如果可以写上，保证代码的可读性。
别名：
表别名，保证简介和清晰
sql> select t.t_name, tc.begin_date, tc.days from join_teacher as t
inner join join_teacher_class as tc where t.id=tc.t_id and tc.days > 15;
t_name | begin_date | days |
+--------+------------+------+
| 韩信 | 2013-02-28 | 18 |
| 韩信 | 2013-03-31 | 22 |
| 李白 | 2013-02-22 | 20 |
| 李白 | 2013-03-31 | 22 |
+--------+------------+------+
4 rows in set (0.00 sec)
列别名：
select t.id, tc.id, t.t_name, tc.begin_date, tc.days from join_teacher
as t inner join join_teacher_class as tc where t.id=tc.t_id and
tc.days > 15;
mysql> select t.id, tc.id, t.t_name, tc.begin_date, tc.days from
join_teacher as t inner join join_teacher_class as tc where
t.id=tc.t_id and tc.days > 15;
+----+----+--------+------------+------+
| id | id | t_name | begin_date | days |
+----+----+--------+------------+------+
| 1 | 2 | 韩信 | 2013-02-28 | 18 |
| 1 | 3 | 韩信 | 2013-03-31 | 22 |
| 2 | 4 | 李白 | 2013-02-22 | 20 |
| 2 | 5 | 李白 | 2013-03-31 | 22 |
+----+----+--------+------------+------+
4 rows in set (0.00 sec)
select t.id as t_id, tc.id as tc_id, t.t_name, tc.begin_date, tc.days
from join_teacher as t inner join join_teacher_class as tc where
t.id=tc.t_id and tc.days > 15;
mysql> select t.id as t_id, tc.id as tc_id, t.t_name, tc.begin_date,
tc.days from join_teacher as t inner join join_teacher_class as tc
where t.id=tc.t_id and tc.days > 15;
+------+-------+--------+------------+------+
| t_id | tc_id | t_name | begin_date | days |
+------+-------+--------+------------+------+
| 1 | 2 | 韩信 | 2013-02-28 | 18 |
| 1 | 3 | 韩信 | 2013-03-31 | 22 |
| 2 | 4 | 李白 | 2013-02-22 | 20 |
| 2 | 5 | 李白 | 2013-03-31 | 22 |
+------+-------+--------+------------+------+
4 rows in set (0.00 sec)
外连接：
分类：
左外连接
右外连接
全外连接 （mysql暂不支持）
左连接：
在连接时，如果出现左边表，数据连接不到右边表的情况，则左边表的数据在最终结
果内被保留。而如果出现右表数据连接不到左表的情况，右表数据被丢弃。
select t.id as t_id, tc.id as tc_id, t.t_name, tc.begin_date,
tc.days from join_teacher as t left join join_teacher_class as tc
on t.id=tc.t_id;
mysql> select t.id as t_id, tc.id as tc_id, t.t_name, tc.begin_date,
-> tc.days from join_teacher as t left join join_teacher_class as
tc
-> on t.id=tc.t_id;
+------+-------+-----------+------------+------+
| t_id | tc_id | t_name | begin_date | days |
+------+-------+-----------+------------+------+
| 1 | 1 | 韩信 | 2013-01-15 | 15 |
| 1 | 2 | 韩信 | 2013-02-28 | 18 |
| 1 | 3 | 韩信 | 2013-03-31 | 22 |
| 1 | 7 | 韩信 | 2013-04-19 | 15 |
| 2 | 4 | 李白 | 2013-02-22 | 20 |
| 2 | 5 | 李白 | 2013-03-31 | 22 |
| 2 | 9 | 李白 | 2013-05-04 | 5 |
| 3 | 6 | 韩非子 | 2013-03-27 | 15 |
| 3 | 8 | 韩非子 | 2013-05-28 | 15 |
| 4 | NULL | 孙武 | NULL | NULL |
+------+-------+-----------+------------+------+
10 rows in set (0.00 sec)
drop table if exists one;
create table one(
one_id int,
one_data char(1),
public_field int
);
insert into one values
(1,'a',10),
(2,'b',20),
(3,'c',30);
drop table if exists two;
create table two(
two_id int,
two_data char(1) not null default 't',
public_field int
);
insert into two values
(2,'B',20),
(3,'C',30),
(4,'D',40);
左连接：
select * from one left join two on one_id=two_id;
mysql> select * from one left join two on one_id=two_id;
+--------+----------+--------------+--------+----------+--------------+
| one_id | one_data | public_field | two_id | two_data | public_field |
+--------+----------+--------------+--------+----------+--------------+
| 1 | a | 10 | NULL | NULL | NULL |
| 2 | b | 20 | 2 | B | 20 |
| 3 | c | 30 | 3 | C | 30 |
+--------+----------+--------------+--------+----------+--------------+
3 rows in set (0.00 sec)
右连接：
select * from one right join two on one_id=two_id;
mysql> select * from one right join two on one_id=two_id;
+--------+----------+--------------+--------+----------+--------------+
| one_id | one_data | public_field | two_id | two_data | public_field |
+--------+----------+--------------+--------+----------+--------------+
| 2 | b | 20 | 2 | B | 20 |
| 3 | c | 30 | 3 | C | 30 |
| NULL | NULL | NULL | 4 | D | 40 |
+--------+----------+--------------+--------+----------+--------------+
3 rows in set (0.00 sec)
内链接：
select * from one inner join two on one_id=two_id;
mysql> select * from one inner join two on one_id=two_id;
+--------+----------+--------------+--------+----------+--------------+
| one_id | one_data | public_field | two_id | two_data | public_field |
+--------+----------+--------------+--------+----------+--------------+
| 2 | b | 20 | 2 | B | 20 |
| 3 | c | 30 | 3 | C | 30 |
+--------+----------+--------------+--------+----------+--------------+
2 rows in set (0.00 sec)
左连接+右连接 = 全外连接
mysql> (select * from one left join two on one_id=two_id)
-> union
-> (select * from one right join two on one_id=two_id);
+--------+----------+--------------+--------+----------+--------------+
| one_id | one_data | public_field | two_id | two_data | public_field |
+--------+----------+--------------+--------+----------+--------------+
| 1 | a | 10 | NULL | NULL | NULL |
| 2 | b | 20 | 2 | B | 20 |
| 3 | c | 30 | 3 | C | 30 |
| NULL | NULL | NULL | 4 | D | 40 |
+--------+----------+--------------+--------+----------+--------------+
4 rows in set (0.00 sec)
using会去掉重复字段，并且会放在最前一列，建议使用，因为去掉重复对人友好
select * from one left join two using (public_field);
mysql> select * from one left join two using (public_field);
+--------------+--------+----------+--------+----------+
| public_field | one_id | one_data | two_id | two_data |
+--------------+--------+----------+--------+----------+
| 10 | 1 | a | NULL | NULL |
| 20 | 2 | b | 2 | B |
| 30 | 3 | c | 3 | C |
+--------------+--------+----------+--------+----------+
3 rows in set (0.00 sec)
select * from one left join two on one.public_field=two.public_field;
mysql> select * from one left join two on
one.public_field=two.public_field;
+--------+----------+--------------+--------+----------+--------------+
| one_id | one_data | public_field | two_id | two_data | public_field |
+--------+----------+--------------+--------+----------+--------------+
| 1 | a | 10 | NULL | NULL | NULL |
| 2 | b | 20 | 2 | B | 20 |
| 3 | c | 30 | 3 | C | 30 |
+--------+----------+--------------+--------+----------+--------------+
3 rows in set (0.00 sec)
=======================lession30=自然连接==============================
自然连接：
通过mysql自己的判断完成连接过程：
不需要指定连接条件
mysql会使用多表内的，相同的字段，作为连接条件。
select * from one natural join two; 相当于
select * from one inner join two using(public_field);
mysql> select * from one natural join two;
+--------------+--------+----------+--------+----------+
| public_field | one_id | one_data | two_id | two_data |
+--------------+--------+----------+--------+----------+
| 20 | 2 | b | 2 | B |
| 30 | 3 | c | 3 | C |
+--------------+--------+----------+--------+----------+
2 rows in set (0.01 sec)
mysql> select * from one inner join two using(public_field);
+--------------+--------+----------+--------+----------+
| public_field | one_id | one_data | two_id | two_data |
+--------------+--------+----------+--------+----------+
| 20 | 2 | b | 2 | B |
| 30 | 3 | c | 3 | C |
+--------------+--------+----------+--------+----------+
2 rows in set (0.00 sec)
自然连接分成内外之分：
内，natural join
外，左外，右外 (左右是相对与join来说的)
natural letf join
natural right join
select * from one natural left join two;相当于
select * from one left join two using (public_field);
mysql> select * from one natural left join two;
+--------------+--------+----------+--------+----------+
| public_field | one_id | one_data | two_id | two_data |
+--------------+--------+----------+--------+----------+
| 10 | 1 | a | NULL | NULL |
| 20 | 2 | b | 2 | B |
| 30 | 3 | c | 3 | C |
+--------------+--------+----------+--------+----------+
3 rows in set (0.00 sec)
mysql> select * from one left join two using (public_field);
+--------------+--------+----------+--------+----------+
| public_field | one_id | one_data | two_id | two_data |
+--------------+--------+----------+--------+----------+
| 10 | 1 | a | NULL | NULL |
| 20 | 2 | b | 2 | B |
| 30 | 3 | c | 3 | C |
+--------------+--------+----------+--------+----------+
3 rows in set (0.00 sec)
select * from one natural right join two;相当于
select * from one right join two using(public_field);
mysql> select * from one natural right join two;
+--------------+--------+----------+--------+----------+
| public_field | two_id | two_data | one_id | one_data |
+--------------+--------+----------+--------+----------+
| 20 | 2 | B | 2 | b |
| 30 | 3 | C | 3 | c |
| 40 | 4 | D | NULL | NULL |
+--------------+--------+----------+--------+----------+
3 rows in set (0.00 sec)
mysql> select * from one right join two using(public_field);
+--------------+--------+----------+--------+----------+
| public_field | two_id | two_data | one_id | one_data |
+--------------+--------+----------+--------+----------+
| 20 | 2 | B | 2 | b |
| 30 | 3 | C | 3 | c |
| 40 | 4 | D | NULL | NULL |
+--------------+--------+----------+--------+----------+
3 rows in set (0.00 sec)
info_class; id, class_name.
info_student; id,student_name, class_id.
info_student_info: id, student_detail.
作业：
连接时支持多表连接：
select s.*, si.* from info_class as c left join info_student as s on
c.id = s.class_id left join info_student_info as si on s.id = si.id
where c.class_name='php0331';
作业2：许多著名公司的面试题
参考图片：
L30自然连接后的作业2.JPG
提示：
Match left join class on match.host_id=class.id left join class on
match.guest_id=class.id
mysql> drop table if exists class;
mysql> create table class(
-> id tinyint primary key auto_increment,
-> class_name char(7)
-> )character set utf8;
Query OK, 0 rows affected (0.10 sec)
mysql> insert into class values
-> (2,'php0331'),
-> (5,'php0228'),
-> (1,'php0115'),
-> (7,'php0505');
Query OK, 4 rows affected (0.05 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> select * from class;
+----+------------+
| id | class_name |
+----+------------+
| 2 | php0331 |
| 5 | php0228 |
| 1 | php0115 |
| 7 | php0505 |
+----+------------+
4 rows in set (0.12 sec)
// match应该是mysql的关键字创建的时候老出现问题
mysql> create table match( id tinyint primary key auto_increment,
host_id tinyint, guest_id tinyint, match_time date, match_result
char(7) )character set utf8;
ERROR 1064 (42000): You have an error in your SQL syntax; check the
manual that corresponds to your MySQL server version for the right
syntax to use near 'match( id tinyint primary key auto_increment,
host_id tinyint, guest_id tinyint,' at line 1
mysql> create table game(
id tinyint primary key auto_increment,
host_id tinyint,
guest_id tinyint,
match_time date,
match_result char(7) )character set utf8;
Query OK, 0 rows affected (0.01 sec)
mysql> insert into game values
(null,2,1,'2013-04-09','34:28'),
(null,2,7,'2013-03-09','35:45');
Query OK, 2 rows affected (0.02 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> select * from game;
+----+---------+----------+------------+--------------+
| id | host_id | guest_id | match_time | match_result |
+----+---------+----------+------------+--------------+
| 1 | 2 | 1 | 2013-04-09 | 34:28 |
| 2 | 2 | 1 | 2013-04-09 | 34:28 |
| 3 | 2 | 7 | 2013-03-09 | 35:45 |
+----+---------+----------+------------+--------------+
3 rows in set (0.00 sec)
l> delete from game where id = 1;
Query OK, 1 row affected (0.05 sec)
mysql> select * from game;
+----+---------+----------+------------+--------------+
| id | host_id | guest_id | match_time | match_result |
+----+---------+----------+------------+--------------+
| 2 | 2 | 1 | 2013-04-09 | 34:28 |
| 3 | 2 | 7 | 2013-03-09 | 35:45 |
+----+---------+----------+------------+--------------+
2 rows in set (0.00 sec)
mysql> select c.class_name,c2.class_name,g.match_time,g.match_result
from
-> game as g left join class as c on g.host_id=c.id
-> left join class as c2 on g.guest_id=c2.id;
+------------+------------+------------+--------------+
| class_name | class_name | match_time | match_result |
+------------+------------+------------+--------------+
| php0331 | php0115 | 2013-04-09 | 34:28 |
| php0331 | php0505 | 2013-03-09 | 35:45 |
+------------+------------+------------+--------------+
2 rows in set (0.00 sec)
mysql> select c.class_name,c2.class_name, g.match_time, g.match_result
from game as g left join class as c on g.host_id=c.id left join class
as c2 on g.guest_id=c2.id limit 1;
+------------+------------+------------+--------------+
| class_name | class_name | match_time | match_result |
+------------+------------+------------+--------------+
| php0331 | php0115 | 2013-04-09 | 34:28 |
+------------+------------+------------+--------------+
1 row in set (0.00 sec)
作业3：
参考图片：L30自然连接后的作业3.JPG
1.获得所有的顶级部门（即parent_id = 0）
2.获得教学部内所有的子部门。(法1，用subquery；法2 用(2)join)
mysql> create table dept(
-> id tinyint primary key auto_increment,
-> dept_name char(9),
-> parent_id tinyint
-> )character set utf8;
Query OK, 0 rows affected (0.00 sec)
1.获得所有顶级部门
mysql> select * from dept where parent_id=0;
+----+-----------+-----------+
| id | dept_name | parent_id |
+----+-----------+-----------+
| 1 | 行政部 | 0 |
| 2 | 教学部 | 0 |
+----+-----------+-----------+
2 rows in set (0.04 sec)
2.获得教学部内所有的子部门
法一：subquery
mysql> select * from dept where parent_id=
-> (select id from dept where dept_name='教学部');
+----+-----------+-----------+
| id | dept_name | parent_id |
+----+-----------+-----------+
| 3 | php | 2 |
| 4 | java | 2 |
| 5 | .net | 2 |
| 6 | 平面 | 2 |
+----+-----------+-----------+
4 rows in set (0.00 sec)
法二：join
mysql> select * from dept as son inner join dept as pa on
(son.parent_id=pa.id and pa.dept_name='教学部');
+----+-----------+-----------+----+-----------+-----------+
| id | dept_name | parent_id | id | dept_name | parent_id |
+----+-----------+-----------+----+-----------+-----------+
| 3 | php | 2 | 2 | 教学部 | 0 |
| 4 | java | 2 | 2 | 教学部 | 0 |
| 5 | .net | 2 | 2 | 教学部 | 0 |
| 6 | 平面 | 2 | 2 | 教学部 | 0 |
+----+-----------+-----------+----+-----------+-----------+
4 rows in set (0.02 sec)
优化：
mysql> select son.id,son.dept_name,pa.dept_name from dept as son inner
join dept as pa on (son.parent_id=pa.id and pa.dept_name='教学部');
+----+-----------+-----------+
| id | dept_name | dept_name |
+----+-----------+-----------+
| 3 | php | 教学部 |
| 4 | java | 教学部 |
| 5 | .net | 教学部 |
| 6 | 平面 | 教学部 |
+----+-----------+-----------+
在优化：（改了教学部dept_name为parent）
mysql> select son.id,son.dept_name,pa.dept_name as parent from dept as
son inner join dept as pa on (son.parent_id=pa.id and
pa.dept_name='教学部');
+----+-----------+-----------+
| id | dept_name | parent |
+----+-----------+-----------+
| 3 | php | 教学部 |
| 4 | java | 教学部 |
| 5 | .net | 教学部 |
| 6 | 平面 | 教学部 |
+----+-----------+-----------+
4 rows in set (0.00 sec)
4 rows in set (0.00 sec)
注意：如果不是inner join的话，会保留所有哦比如
mysql> select * from dept as son left join dept as pa on
-> (son.parent_id=pa.id and pa.dept_name='教学部');
+----+-----------+-----------+------+-----------+-----------+
| id | dept_name | parent_id | id | dept_name | parent_id |
+----+-----------+-----------+------+-----------+-----------+
| 1 | 行政部 | 0 | NULL | NULL | NULL |
| 2 | 教学部 | 0 | NULL | NULL | NULL |
| 3 | php | 2 | 2 | 教学部 | 0 |
| 4 | java | 2 | 2 | 教学部 | 0 |
| 5 | .net | 2 | 2 | 教学部 | 0 |
| 6 | 平面 | 2 | 2 | 教学部 | 0 |
| 7 | 咨询 | 1 | NULL | NULL | NULL |
| 8 | 财务 | 1 | NULL | NULL | NULL |
+----+-----------+-----------+------+-----------+-----------+
8 rows in set (0.00 sec)
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