# 转载:http://www.cnblogs.com/yuanchenqi/articles/6357507.html
# 外键：一种约束条件，与主键对应
# 主表：被绑定的表；字表
# 外键约束：
# -- 每一个班主任会对应多个学生 , 而每个学生只能对应一个班主任
#
# ----主表
#
# CREATE TABLE ClassCharger(
#
# id TINYINT PRIMARY KEY auto_increment,
# name VARCHAR (20),
# age INT ,
# is_marriged boolean -- show create table ClassCharger: tinyint(1)
#
# );
#
# INSERT INTO ClassCharger (name,age,is_marriged) VALUES ("冰冰",12,0),
# ("丹丹",14,0),
# ("歪歪",22,0),
# ("姗姗",20,0),
# ("小雨",21,0);
#
#
# ----子表
#
# CREATE TABLE Student(
#
# id INT PRIMARY KEY auto_increment,
# name VARCHAR (20),
# charger_id TINYINT, --切记:作为外键一定要和关联主键的数据类型保持一致
# -- [ADD CONSTRAINT charger_fk_stu]FOREIGN KEY (charger_id) REFERENCES ClassCharger(id)
#
# ) ENGINE=INNODB;
#
# INSERT INTO Student(name,charger_id) VALUES ("alvin1",2),
# ("alvin2",4),
# ("alvin3",1),
# ("alvin4",3),
# ("alvin5",1),
# ("alvin6",3),
# ("alvin7",2);
#
#
# DELETE FROM ClassCharger WHERE name="冰冰";
# INSERT student (name,charger_id) VALUES ("yuan",1);
# -- 删除居然成功,可是 alvin3显示还是有班主任id=1的冰冰的;
#
# -----------增加外键和删除外键---------
#
# ALTER TABLE student ADD CONSTRAINT abc
# FOREIGN KEY(charger_id)
# REFERENCES classcharger(id);
#
#
# ALTER TABLE student DROP FOREIGN KEY abc;
#————————————————————————————————————————————————————#
# --外键约束对子表的含义: 如果在父表中找不到候选键,则不允许在子表上进行insert/update
#
# --外键约束对父表的含义: 在父表上进行update/delete以更新或删除在子表中有一条或多条对
# -- 应匹配行的候选键时,父表的行为取决于：在定义子表的外键时指定的
# -- on update/on delete子句
# -----------------innodb支持的四种方式---------------------------------------
#
# -----cascade方式 在父表上update/delete记录时，同步update/delete掉子表的匹配记录
# -----外键的级联删除：如果父表中的记录被删除，则子表中对应的记录自动被删除--------
#
# FOREIGN KEY (charger_id) REFERENCES ClassCharger(id)
# ON DELETE CASCADE
#
# ------set null方式 在父表上update/delete记录时，将子表上匹配记录的列设为null
# -- 要注意子表的外键列不能为not null
#
# FOREIGN KEY (charger_id) REFERENCES ClassCharger(id)
# ON DELETE SET NULL
#
#
# ------Restrict方式 :拒绝对父表进行删除更新操作(了解)
#
# ------No action方式 在mysql中同Restrict,如果子表中有匹配的记录,则不允许对父表对应候选键
# -- 进行update/delete操作（了解）
#————————————————————————————————————————————————————#
# 多表查询
# -- 准备两张表
# -- company.employee
# -- company.department
#
# create table employee(
# emp_id int auto_increment primary key not null,
# emp_name varchar(50),
# age int,
# dept_id int
# );
#
# insert into employee(emp_name,age,dept_id) values
# ('A',19,200),
# ('B',26,201),
# ('C',30,201),
# ('D',24,202),
# ('E',20,200),
# ('F',38,204);
#
#
# create table department(
# dept_id int,
# dept_name varchar(100)
# );
#
# insert into department values
# (200,'人事部'),
# (201,'技术部'),
# (202,'销售部'),
# (203,'财政部');
#
# mysql> select * from employee;
# +--------+----------+------+---------+
# | emp_id | emp_name | age | dept_id |
# +--------+----------+------+---------+
# | 1 | A | 19 | 200 |
# | 2 | B | 26 | 201 |
# | 3 | C | 30 | 201 |
# | 4 | D | 24 | 202 |
# | 5 | E | 20 | 200 |
# | 6 | F | 38 | 204 |
# +--------+----------+------+---------+
# rows in set (0.00 sec)
#
# mysql> select * from department;
# +---------+-----------+
# | dept_id | dept_name |
# +---------+-----------+
# | 200 | 人事部 |
# | 201 | 技术部 |
# | 202 | 销售部 |
# | 203 | 财政部 |
# +---------+-----------+
# rows in set (0.01 sec)
#————————————————————————————————————————————————————#
# 1.笛卡尔积查询
# mysql> SELECT * FROM employee,department;
#
# -- select employee.emp_id,employee.emp_name,employee.age,
# -- department.dept_name from employee,department;
#
# +--------+----------+------+---------+---------+-----------+
# | emp_id | emp_name | age | dept_id | dept_id | dept_name |
# +--------+----------+------+---------+---------+-----------+
# | 1 | A | 19 | 200 | 200 | 人事部 |
# | 1 | A | 19 | 200 | 201 | 技术部 |
# | 1 | A | 19 | 200 | 202 | 销售部 |
# | 1 | A | 19 | 200 | 203 | 财政部 |
# | 2 | B | 26 | 201 | 200 | 人事部 |
# | 2 | B | 26 | 201 | 201 | 技术部 |
# | 2 | B | 26 | 201 | 202 | 销售部 |
# | 2 | B | 26 | 201 | 203 | 财政部 |
# | 3 | C | 30 | 201 | 200 | 人事部 |
# | 3 | C | 30 | 201 | 201 | 技术部 |
# | 3 | C | 30 | 201 | 202 | 销售部 |
# | 3 | C | 30 | 201 | 203 | 财政部 |
# | 4 | D | 24 | 202 | 200 | 人事部 |
# | 4 | D | 24 | 202 | 201 | 技术部 |
# | 4 | D | 24 | 202 | 202 | 销售部 |
# | 4 | D | 24 | 202 | 203 | 财政部 |
# | 5 | E | 20 | 200 | 200 | 人事部 |
# | 5 | E | 20 | 200 | 201 | 技术部 |
# | 5 | E | 20 | 200 | 202 | 销售部 |
# | 5 | E | 20 | 200 | 203 | 财政部 |
# | 6 | F | 38 | 204 | 200 | 人事部 |
# | 6 | F | 38 | 204 | 201 | 技术部 |
# | 6 | F | 38 | 204 | 202 | 销售部 |
# | 6 | F | 38 | 204 | 203 | 财政部 |
# +--------+----------+------+---------+---------+-----------+
# 2.内连接
# -- 查询两张表中都有的关联数据,相当于利用条件从笛卡尔积结果中筛选出了正确的结果。
#
# select * from employee,department where employee.dept_id = department.dept_id;
# --select * from employee inner join department on employee.dept_id = department.dept_id;
#
# +--------+----------+------+---------+---------+-----------+
# | emp_id | emp_name | age | dept_id | dept_id | dept_name |
# +--------+----------+------+---------+---------+-----------+
# | 1 | A | 19 | 200 | 200 | 人事部 |
# | 2 | B | 26 | 201 | 201 | 技术部 |
# | 3 | C | 30 | 201 | 201 | 技术部 |
# | 4 | D | 24 | 202 | 202 | 销售部 |
# | 5 | E | 20 | 200 | 200 | 人事部 |
# +--------+----------+------+---------+---------+-----------+
# 3.外连接
# --（1）左外连接：在内连接的基础上增加左边有右边没有的结果
#
# select *
# from employee left
#
# join
# department
# on
# employee.dept_id = department.dept_id;
#
# +--------+----------+------+---------+---------+-----------+
# | emp_id | emp_name | age | dept_id | dept_id | dept_name |
# +--------+----------+------+---------+---------+-----------+
# | 1 | A | 19 | 200 | 200 | 人事部 |
# | 5 | E | 20 | 200 | 200 | 人事部 |
# | 2 | B | 26 | 201 | 201 | 技术部 |
# | 3 | C | 30 | 201 | 201 | 技术部 |
# | 4 | D | 24 | 202 | 202 | 销售部 |
# | 6 | F | 38 | 204 | NULL | NULL |
# +--------+----------+------+---------+---------+-----------+
#
# --（2）右外连接：在内连接的基础上增加右边有左边没有的结果
#
# select *
# from employee RIGHT
#
# JOIN
# department
# on
# employee.dept_id = department.dept_id;
#
# +--------+----------+------+---------+---------+-----------+
# | emp_id | emp_name | age | dept_id | dept_id | dept_name |
# +--------+----------+------+---------+---------+-----------+
# | 1 | A | 19 | 200 | 200 | 人事部 |
# | 2 | B | 26 | 201 | 201 | 技术部 |
# | 3 | C | 30 | 201 | 201 | 技术部 |
# | 4 | D | 24 | 202 | 202 | 销售部 |
# | 5 | E | 20 | 200 | 200 | 人事部 |
# | NULL | NULL | NULL | NULL | 203 | 财政部 |
# +--------+----------+------+---------+---------+-----------+
#
# --（3）全外连接：在内连接的基础上增加左边有右边没有的和右边有左边没有的结果
#
# -- mysql不支持全外连接
# full
# JOIN
# -- mysql可以使用此种方式间接实现全外连接
#
# select *
# from employee RIGHT
#
# JOIN
# department
# on
# employee.dept_id = department.dept_id
# UNION
# select *
# from employee LEFT
#
# JOIN
# department
# on
# employee.dept_id = department.dept_id;
#
# +--------+----------+------+---------+---------+-----------+
# | emp_id | emp_name | age | dept_id | dept_id | dept_name |
# +--------+----------+------+---------+---------+-----------+
# | 1 | A | 19 | 200 | 200 | 人事部 |
# | 2 | B | 26 | 201 | 201 | 技术部 |
# | 3 | C | 30 | 201 | 201 | 技术部 |
# | 4 | D | 24 | 202 | 202 | 销售部 |
# | 5 | E | 20 | 200 | 200 | 人事部 |
# | NULL | NULL | NULL | NULL | 203 | 财政部 |
# | 6 | F | 38 | 204 | NULL | NULL |
# +--------+----------+------+---------+---------+-----------+
#
# -- 注意
# union与union
# all的区别：union会去掉相同的纪录
#————————————————————————————————————————————————————#
# 多表查询之复合条件连接查询
# -- 查询员工年龄大于等于25岁的部门
#
# SELECT DISTINCT department.dept_name
# FROM employee,department
# WHERE employee.dept_id = department.dept_id
# AND age>25;
#
#
# --以内连接的方式查询employee和department表，并且以age字段的升序方式显示
#
# select employee.emp_id,employee.emp_name,employee.age,department.dept_name
# from employee,department
# where employee.dept_id = department.dept_id
# order by age asc;
#————————————————————————————————————————————————————#
# 多表查询之子查询
# -- 子查询是将一个查询语句嵌套在另一个查询语句中。
# -- 内层查询语句的查询结果，可以为外层查询语句提供查询条件。
# -- 子查询中可以包含：IN、NOT IN、ANY、ALL、EXISTS 和 NOT EXISTS等关键字
# -- 还可以包含比较运算符：= 、 !=、> 、<等
#
#
# -- 1. 带IN关键字的子查询
#
# ---查询employee表，但dept_id必须在department表中出现过
#
# select * from employee
# where dept_id IN
# (select dept_id from department);
#
#
# +--------+----------+------+---------+
# | emp_id | emp_name | age | dept_id |
# +--------+----------+------+---------+
# | 1 | A | 19 | 200 |
# | 2 | B | 26 | 201 |
# | 3 | C | 30 | 201 |
# | 4 | D | 24 | 202 |
# | 5 | E | 20 | 200 |
# +--------+----------+------+---------+
# rows in set (0.01 sec)
#
#
#
# -- 2. 带比较运算符的子查询
# -- =、!=、>、>=、<、<=、<>
#
# -- 查询员工年龄大于等于25岁的部门
# select dept_id,dept_name from department
# where dept_id IN
# (select DISTINCT dept_id from employee where age>=25);
#
# -- 3. 带EXISTS关键字的子查询
#
# -- EXISTS关字键字表示存在。在使用EXISTS关键字时，内层查询语句不返回查询的记录。
# -- 而是返回一个真假值。Ture或False
# -- 当返回Ture时，外层查询语句将进行查询；当返回值为False时，外层查询语句不进行查询
#
# select * from employee
# WHERE EXISTS
# (SELECT dept_name from department where dept_id=203);
#
# --department表中存在dept_id=203，Ture
#
#
# select * from employee
# WHERE EXISTS
# (SELECT dept_name from department where dept_id=205);
#
# -- Empty set (0.00 sec)
#
#
# ps: create table t1(select * from t2);
Pyhton学习——Day47
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