mysql命令用法复习笔记

mysql命令用法复习笔记

 

show DATABASES ;

create database nulige character set utf8;

use nulige;

show tables;

#创建表
CREATE TABLE ExamResult(

   id INT PRIMARY KEY  auto_increment,
   name VARCHAR (20),
   JS DOUBLE ,
   Django DOUBLE ,
   flask DOUBLE
);


#往表中插入数据
INSERT INTO ExamResult VALUES  (1,"yuan",98,98,98),
                               (2,"xialv",35,98,67),
                               (3,"alex",59,59,62),
                               (4,"wusir",88,89,82),
                               (5,"alvin",88,98,67),
                               (6,"yuan",86,100,55);

#查询表中所有学生的信息
select * from ExamResult;

#查询表中所有学生的姓名和对应的英语成绩
SELECT name,JS FROM ExamResult;

#过滤表中重复数据
select DISTINCT Js,name from ExamResult;


SELECT name,JS,Django,flask FROM ExamResult;


SELECT name,JS+10,Django+10,flask+20 FROM ExamResult;


SELECT name as 姓名,JS+10 as JS成绩,Django+10,flask+20 FROM ExamResult;


SELECT name JS from ExamResult;

select * from ExamResult WHERE name='yuan'

SELECT name,Js from ExamResult WHERE JS>90;

SELECT name,JS from ExamResult WHERE JS!=88;

#between在什么之间  在88=100之间
SELECT name,JS FROM ExamResult WHERE JS BETWEEN 88 and 100;

#in在什么之内
SELECT name,JS FROM ExamResult WHERE JS IN (88,99,77);

#like 模糊查询，查询名字内有y的同学
SELECT name,JS FROM ExamResult WHERE name LIKE "y%";


SELECT name,JS FROM ExamResult WHERE name LIKE "a____";

#查询js分=98同学
SELECT name,JS from ExamResult WHERE name='yuan' and JS=98;


insert into ExamResult (name) VALUE ('刘洋');

SELECT * from ExamResult;

#查询值为空
SELECT name from ExamResult WHERE JS is NULL;


#排序
SELECT name,JS from ExamResult WHERE JS>70 ORDER BY JS;

SELECT name,JS FROM ExamResult WHERE JS>70 ORDER BY Js DESC ;

#as重命名
SELECT name,JS+Django+flask as 总成绩 from ExamResult ORDER BY 总成绩 DESC;

#按yuan 总成绩进行降序排列（mysql语句有执行顺序：from where select group by having order by)
SELECT name,JS+Django+flask as 总成绩 from ExamResult WHERE name="yuan" ORDER BY 总成绩;


#分组查询 group by
SELECT * from ExamResult;

#按名字进行分组
SELECT * from ExamResult GROUP BY name;

#按JS进行分组
SELECT * from ExamResult GROUP BY JS;

#按第3列进行分组
SELECT * from ExamResult GROUP BY 3;

#按名字进行排序
SELECT name,sum(JS) from ExamResult GROUP BY name;

#对成绩表按名字分组后，显示每一类名字的Django的分数总和>150的
SELECT name,sum(Django) from ExamResult GROUP BY name having sum(Django)>150;

#having和where两者都可以对查询结果进行进一步的过滤，差别有：
# <1>where语句只能用在分组之前的筛选，having可以用在分组之后的筛选；
# <2>使用where语句的地方都可以用having进行替换
# <3>having中可以用聚合函数，where中就不行。

SELECT * from ExamResult WHERE id=3;
SELECT * from ExamResult HAVING id=3;

#聚合函数：先把要求的内容查出来再包上聚合函数即可。

#count(列名)：统计行的个数
SELECT count(name) from ExamResult WHERE js>70;

#统计一个班级共有多少学生
select count(*) from ExamResult;

SELECT sum(JS)/count(name) from ExamResult;

SELECT AVG(JS) from ExamResult;


#遇到ifnull的时候转换成0
#统计总分大于280的人数有多少？
select count(name) from ExamResult where (ifnull(JS,0)+ifnull(Django,0)+ifnull(flask,0))>280;


SELECT * from ExamResult;

#max最大值
SELECT max(JS) FROM ExamResult;

#遇到null的时候，就转成0
#min最小值
SELECT min(ifnull(JS,0)) FROM ExamResult;
SELECT max(JS+Django+flask) from ExamResult;

#limit 跳过几条显示几条
SELECT * FROM  ExamResult LIMIT 1;

#跳过1,从2开始到5
SELECT * FROM  ExamResult LIMIT 1,4;

增加外键

#查看数据库
mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| lessens            |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set


#创建abc数据库
mysql> create database abc character set utf8;
Query OK, 1 row affected


#进入abc表
mysql> use abc ;
Database changed

#创建表
mysql> CREATE TABLE ClassCharger(

       id TINYINT PRIMARY KEY auto_increment,
       name VARCHAR (20),
       age INT ,
       is_marriged boolean
)ENGINE=INNODB;
Query OK, 0 rows affected

#往表中插入数据
mysql> INSERT INTO ClassCharger (name,age,is_marriged) VALUES ("冰冰",52,0),
                                                       ("丹丹",34,0),
                                                       ("歪歪",32,0),
                                                       ("姗姗",28,0),
                                                       ("小雨",61,0);
Query OK, 5 rows affected
Records: 5  Duplicates: 0  Warnings: 0

#创建表
mysql> CREATE TABLE Student(
       id INT PRIMARY KEY auto_increment,
       name VARCHAR (20),
       charger_id TINYINT
) ENGINE=INNODB;
Query OK, 0 rows affected

#往表中插入数据
mysql> INSERT INTO Student(name,charger_id) VALUES ("alvin1",2),
                                            ("alvin2",4),
                                            ("alvin3",1),
                                            ("alvin4",3),
                                            ("alvin5",5);
Query OK, 5 rows affected
Records: 5  Duplicates: 0  Warnings: 0

#查看表中数据
mysql> select * from Student;
+----+--------+------------+
| id | name   | charger_id |
+----+--------+------------+
|  1 | alvin1 |          2 |
|  2 | alvin2 |          4 |
|  3 | alvin3 |          1 |
|  4 | alvin4 |          3 |
|  5 | alvin5 |          5 |
+----+--------+------------+
5 rows in set

#查看表中数据
mysql> select * from ClassCharger;
+----+------+-----+-------------+
| id | name | age | is_marriged |
+----+------+-----+-------------+
|  1 | 冰冰 |  52 |           0 |
|  2 | 丹丹 |  34 |           0 |
|  3 | 歪歪 |  32 |           0 |
|  4 | 姗姗 |  28 |           0 |
|  5 | 小雨 |  61 |           0 |
+----+------+-----+-------------+
5 rows in set

#创建外键
mysql> ALTER TABLE Student  ADD CONSTRAINT abc
                     FOREIGN KEY(charger_id)
                     REFERENCES  classcharger(id);
Query OK, 5 rows affected
Records: 5  Duplicates: 0  Warnings: 0


#查看表结构
mysql> desc Student;
+------------+-------------+------+-----+---------+----------------+
| Field      | Type        | Null | Key | Default | Extra          |
+------------+-------------+------+-----+---------+----------------+
| id         | int(11)     | NO   | PRI | NULL    | auto_increment |
| name       | varchar(20) | YES  |     | NULL    |                |
| charger_id | tinyint(4)  | YES  | MUL | NULL    |                |
+------------+-------------+------+-----+---------+----------------+
3 rows in set

#查看表结构
mysql> desc ClassCharger;
+-------------+-------------+------+-----+---------+----------------+
| Field       | Type        | Null | Key | Default | Extra          |
+-------------+-------------+------+-----+---------+----------------+
| id          | tinyint(4)  | NO   | PRI | NULL    | auto_increment |
| name        | varchar(20) | YES  |     | NULL    |                |
| age         | int(11)     | YES  |     | NULL    |                |
| is_marriged | tinyint(1)  | YES  |     | NULL    |                |
+-------------+-------------+------+-----+---------+----------------+
4 rows in set


#查看建表语句
mysql> show CREATE TABLE Student;
+---------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table   | Create Table                                                                                                                                                                                                                                                                                                                |
+---------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Student | CREATE TABLE `student` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(20) DEFAULT NULL,
  `charger_id` tinyint(4) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `abc` (`charger_id`),
  CONSTRAINT `abc` FOREIGN KEY (`charger_id`) REFERENCES `classcharger` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8 |
+---------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set

mysql> select * from student;
+----+--------+------------+
| id | name | charger_id |
+----+--------+------------+
| 1 | alvin1 | 2 |
| 2 | alvin2 | 4 |
| 3 | alvin3 | 1 |
| 4 | alvin4 | 3 |
| 5 | alvin5 | 5 |
+----+--------+------------+
5 rows in set

#插入数据
mysql> insert into student(name,charger_id) values("alvin1",2),("alvin1",4);
Query OK, 2 rows affected
Records: 2 Duplicates: 0 Warnings: 0

mysql> select * from student;
+----+--------+------------+
| id | name | charger_id |
+----+--------+------------+
| 1 | alvin1 | 2 |
| 2 | alvin2 | 4 |
| 3 | alvin3 | 1 |
| 4 | alvin4 | 3 |
| 5 | alvin5 | 5 |
| 6 | alvin1 | 2 |
| 7 | alvin1 | 4 |
+----+--------+------------+
7 rows in set

#查看表
mysql> show tables;
+---------------+
| Tables_in_abc |
+---------------+
| classcharger |
| student |
+---------------+
2 rows in set

#查看表内容
mysql> select * from classcharger;
+----+------+-----+-------------+
| id | name | age | is_marriged |
+----+------+-----+-------------+
| 1 | 冰冰 | 52 | 0 |
| 2 | 丹丹 | 34 | 0 |
| 3 | 歪歪 | 32 | 0 |
| 4 | 姗姗 | 28 | 0 |
| 5 | 小雨 | 61 | 0 |
+----+------+-----+-------------+
5 rows in set

#查看表内容
mysql> select * from student;
+----+--------+------------+
| id | name | charger_id |
+----+--------+------------+
| 1 | alvin1 | 2 |
| 2 | alvin2 | 4 |
| 3 | alvin3 | 1 |
| 4 | alvin4 | 3 |
| 5 | alvin5 | 5 |
| 6 | alvin1 | 2 |
| 7 | alvin1 | 4 |
+----+--------+------------+
7 rows in set

#更新表中数据
mysql> update student set charger_id=4 where id=1 or id=6;
Query OK, 2 rows affected
Rows matched: 2 Changed: 2 Warnings: 0

mysql> select * from student;
+----+--------+------------+
| id | name | charger_id |
+----+--------+------------+
| 1 | alvin1 | 4 |
| 2 | alvin2 | 4 |
| 3 | alvin3 | 1 |
| 4 | alvin4 | 3 |
| 5 | alvin5 | 5 |
| 6 | alvin1 | 4 |
| 7 | alvin1 | 4 |
+----+--------+------------+
7 rows in set

#删除掉id=2 的 丹丹 ，再插入数据就会报错。
mysql> delete from classcharger where id=2;
Query OK, 1 row affected

mysql> select * from classcharger;
+----+------+-----+-------------+
| id | name | age | is_marriged |
+----+------+-----+-------------+
| 1 | 冰冰 | 52 | 0 |
| 3 | 歪歪 | 32 | 0 |
| 4 | 姗姗 | 28 | 0 |
| 5 | 小雨 | 61 | 0 |
+----+------+-----+-------------+
4 rows in set

再插入数据就会报错
mysql> insert into student (name,charger_id) values("alvin8",2);
1452 - Cannot add or update a child row: a foreign key constraint fails (`abc`.`student`, CONSTRAINT `abc` FOREIGN KEY (`charger_id`) REFERENCES `classcharger` (`id`))

 #删除外键

mysql> alter table student drop foreign key abc;
Query OK, 0 rows affected
Records: 0 Duplicates: 0 Warnings: 0

#查看建表语句

mysql> show create table student;
+---------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+---------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| student | CREATE TABLE `student` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(20) DEFAULT NULL,
`charger_id` tinyint(4) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `abc` (`charger_id`)
) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8 |
+---------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set

#增加外键

mysql> ALTER TABLE student ADD CONSTRAINT abc
FOREIGN KEY(charger_id)
REFERENCES classcharger(id);
Query OK, 7 rows affected
Records: 7 Duplicates: 0 Warnings: 0

#查看增加的外键

mysql> show create table student;
+---------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+---------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| student | CREATE TABLE `student` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(20) DEFAULT NULL,
`charger_id` tinyint(4) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `abc` (`charger_id`),
CONSTRAINT `abc` FOREIGN KEY (`charger_id`) REFERENCES `classcharger` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8 |
+---------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set

INNODB支持的ON语句

#查看数据库
mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| abc                |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set

#创建数据库并设置字符集
mysql> create database s1 character set utf8;
Query OK, 1 row affected

mysql> use s1;
Database changed

#创建表cc
mysql> CREATE TABLE CC(

       id TINYINT PRIMARY KEY auto_increment,
       name VARCHAR (20),
       age INT ,
       is_marriged boolean
);
Query OK, 0 rows affected

#创建表s3，并设置外键为 delete cascade 方式
mysql>  create table s3(
     id int primary key auto_increment,
     name varchar(20),
     charger_id tinyint,
     foreign key (charger_id) references CC(id) on delete cascade
     ) engine=innodb;
Query OK, 0 rows affected

#往表中插入数据
mysql> INSERT INTO CC (name,age,is_marriged) VALUES ("冰冰",52,0),
                                             ("丹丹",34,0),
                                             ("歪歪",32,0),
                                             ("姗姗",28,0),
                                             ("小雨",61,0);
Query OK, 5 rows affected
Records: 5  Duplicates: 0  Warnings: 0

#往表中插入数据
mysql> INSERT INTO S3(name,charger_id) VALUES ("alvin1",2),
                                        ("alvin2",4),
                                        ("alvin3",1),
                                        ("alvin4",3),
                                        ("alvin5",5);
Query OK, 5 rows affected
Records: 5  Duplicates: 0  Warnings: 0

#查看表内容
mysql> select * from cc;
+----+------+-----+-------------+
| id | name | age | is_marriged |
+----+------+-----+-------------+
|  1 | 冰冰 |  52 |           0 |
|  2 | 丹丹 |  34 |           0 |
|  3 | 歪歪 |  32 |           0 |
|  4 | 姗姗 |  28 |           0 |
|  5 | 小雨 |  61 |           0 |
+----+------+-----+-------------+
5 rows in set

#查看表内容
mysql> select * from s3;
+----+--------+------------+
| id | name   | charger_id |
+----+--------+------------+
|  1 | alvin1 |          2 |
|  2 | alvin2 |          4 |
|  3 | alvin3 |          1 |
|  4 | alvin4 |          3 |
|  5 | alvin5 |          5 |
+----+--------+------------+
5 rows in set

#删除表中数据
mysql> delete from cc where id=4;
Query OK, 1 row affected

#再查看表内容，4的数据被删除了。
mysql> select * from s3;
+----+--------+------------+
| id | name   | charger_id |
+----+--------+------------+
|  1 | alvin1 |          2 |
|  3 | alvin3 |          1 |
|  4 | alvin4 |          3 |
|  5 | alvin5 |          5 |
+----+--------+------------+
4 rows in set

#查看建表语句
mysql>  show create table s3;
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                                                                                                                                |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| s3    | CREATE TABLE `s3` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(20) DEFAULT NULL,
  `charger_id` tinyint(4) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `charger_id` (`charger_id`),
  CONSTRAINT `s3_ibfk_1` FOREIGN KEY (`charger_id`) REFERENCES `cc` (`id`) ON DELETE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8 |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set



#########################设置外键为 set null 方式#######################

#查看建表语句的外键信息
mysql>  show create table s3;
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                                                                                                                                |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| s3    | CREATE TABLE `s3` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(20) DEFAULT NULL,
  `charger_id` tinyint(4) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `charger_id` (`charger_id`),
  CONSTRAINT `s3_ibfk_1` FOREIGN KEY (`charger_id`) REFERENCES `cc` (`id`) ON DELETE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8 |
+-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set

#删除外键
mysql> alter table s3 drop foreign key s3_ibfk_1;
Query OK, 0 rows affected
Records: 0  Duplicates: 0  Warnings: 0

#查看删除结果
mysql>  show create table s3;
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                                   |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| s3    | CREATE TABLE `s3` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(20) DEFAULT NULL,
  `charger_id` tinyint(4) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `charger_id` (`charger_id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8 |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set

#增加外键为set null 方式
mysql> alter table s3 add constraint s3_fk_cc foreign key (charger_id)
    -> references cc(id) on delete set null;
Query OK, 4 rows affected
Records: 4  Duplicates: 0  Warnings: 0

mysql> select * from cc;
+----+------+-----+-------------+
| id | name | age | is_marriged |
+----+------+-----+-------------+
|  1 | 冰冰 |  52 |           0 |
|  2 | 丹丹 |  34 |           0 |
|  3 | 歪歪 |  32 |           0 |
|  5 | 小雨 |  61 |           0 |
+----+------+-----+-------------+
4 rows in set

mysql> delete from CC where id=3;
Query OK, 1 row affected

mysql> select * from s3;
+----+--------+------------+
| id | name   | charger_id |
+----+--------+------------+
|  1 | alvin1 |          2 |
|  3 | alvin3 |          1 |
|  4 | alvin4 | NULL       |
|  5 | alvin5 |          5 |
+----+--------+------------+
4 rows in set

mysql> 

mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| abc |
| crm |
| mysql |
| performance_schema |
| s1 |
| sys |
+--------------------+
7 rows in set

#创建数据库
mysql> create database t2 character set utf8;
Query OK, 1 row affected

mysql> use t2;
Database changed

#创建表
mysql> create table tableA(id int primary key,name varchar(20));
Query OK, 0 rows affected

#创建表
mysql> create table tableB(id int primary key,name varchar(20),tableA_id int);
Query OK, 0 rows affected

#往表中插入数据
mysql> insert into tableA values(1,'alvin'),(2,'xialv'),
(3,'yuan');
Query OK, 3 rows affected
Records: 3 Duplicates: 0 Warnings: 0

#往表中插入数据
mysql> insert into tableB values(1,'小雨',1),(2,'冰冰',2),(3,'周周',4);
Query OK, 3 rows affected
Records: 3 Duplicates: 0 Warnings: 0

mysql> select * from tableA;
+----+-------+
| id | name |
+----+-------+
| 1 | alvin |
| 2 | xialv |
| 3 | yuan |
+----+-------+
3 rows in set

mysql> select * from tableB;
+----+------+-----------+
| id | name | tableA_id |
+----+------+-----------+
| 1 | 小雨 | 1 |
| 2 | 冰冰 | 2 |
| 3 | 周周 | 4 |
+----+------+-----------+
3 rows in set

#笛卡尔积查询
mysql> select * from tableA,tableB;
+----+-------+----+------+-----------+
| id | name | id | name | tableA_id |
+----+-------+----+------+-----------+
| 1 | alvin | 1 | 小雨 | 1 |
| 2 | xialv | 1 | 小雨 | 1 |
| 3 | yuan | 1 | 小雨 | 1 |
| 1 | alvin | 2 | 冰冰 | 2 |
| 2 | xialv | 2 | 冰冰 | 2 |
| 3 | yuan | 2 | 冰冰 | 2 |
| 1 | alvin | 3 | 周周 | 4 |
| 2 | xialv | 3 | 周周 | 4 |
| 3 | yuan | 3 | 周周 | 4 |
+----+-------+----+------+-----------+
9 rows in set

#内连接查询
mysql> select * from tableA,tableB where tableA.id=tableB.id;
+----+-------+----+------+-----------+
| id | name | id | name | tableA_id |
+----+-------+----+------+-----------+
| 1 | alvin | 1 | 小雨 | 1 |
| 2 | xialv | 2 | 冰冰 | 2 |
| 3 | yuan | 3 | 周周 | 4 |
+----+-------+----+------+-----------+
3 rows in set

#只显示关联人的id,姓名，
mysql> select tableA.id,tableA.name,tableB.name from tableA,tableB where tableA.id=tableB.id;
+----+-------+------+
| id | name | name |
+----+-------+------+
| 1 | alvin | 小雨 |
| 2 | xialv | 冰冰 |
| 3 | yuan | 周周 |
+----+-------+------+
3 rows in set

mysql> select * from tableB inner join tableA on tableB.tableA_id =tableA.id;
+----+------+-----------+----+-------+
| id | name | tableA_id | id | name |
+----+------+-----------+----+-------+
| 1 | 小雨 | 1 | 1 | alvin |
| 2 | 冰冰 | 2 | 2 | xialv |
+----+------+-----------+----+-------+
2 rows in set

#多表查询之连接查询

#创建表
mysql>create table employee(
emp_id int auto_increment primary key not null,
emp_name varchar(50),
age int,
dept_id int
);
Query OK, 0 rows affected

#往表中插入数据
mysql> 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);
Query OK, 6 rows affected
Records: 6 Duplicates: 0 Warnings: 0

#创建表
mysql>create table department(
dept_id int,
dept_name varchar(100)
);
Query OK, 0 rows affected

#往表中插入数据
mysql>insert into department values
(200,'人事部'),
(201,'技术部'),
(202,'销售部'),
(203,'财政部');

Query OK, 4 rows affected
Records: 4 Duplicates: 0 Warnings: 0

#查看表
mysql> show tables;
+--------------+
| Tables_in_t2 |
+--------------+
| department |
| employee |
| tablea |
| tableb |
+--------------+
4 rows in set

#笛卡尔积查询
mysql> select * 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 |
+--------+----------+-----+---------+---------+-----------+
24 rows in set

外连接之左外连接
mysql> 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 |
+--------+----------+-----+---------+---------+-----------+
6 rows in set

mysql> select employee.emp_name,department.dept_name from employee,department where employee.dept_id = department.dept_id and employee.emp_name="A";
+----------+-----------+
| emp_name | dept_name |
+----------+-----------+
| A | 人事部 |
+----------+-----------+
1 row in set

#外连接之右外连接
mysql> 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 |
+--------+----------+------+---------+---------+-----------+
6 rows in set

#外连接之全外连接

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


mysql> select * from tableB full join tableA on tableB.tableA_id = table.id;
1054 - Unknown column 'tableB.tableA_id' in 'on clause'

mysql> select employee.emp_name,department.dept_name from employee,department where employee
-> .dept_id=department.dept_id and department.dept_name="技术部";
+----------+-----------+
| emp_name | dept_name |
+----------+-----------+
| B | 技术部 |
| C | 技术部 |
+----------+-----------+
2 rows in set

#显示大于25岁所有的部门
mysql> select distinct department.dept_name from employee,department where employee.dept_id=department.dept_id and employee.age>25;
+-----------+
| dept_name |
+-----------+
| 技术部 |
+-----------+
1 row in set

多表查询之子查询

#带IN关键字的子查询
mysql> select * from employee where dept_id in(200,201,202,203);
+--------+----------+-----+---------+
| 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 |
+--------+----------+-----+---------+
5 rows in set

mysql> select dept_id from department
;
+---------+
| dept_id |
+---------+
| 200 |
| 201 |
| 202 |
| 203 |
+---------+
4 rows in set

#带IN关键字的子查询
mysql> 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 |
+--------+----------+-----+---------+
5 rows in set

#用select查询语句，建表，会丢失主键信息
mysql> create table aa(select * from employee);
Query OK, 6 rows affected
Records: 6 Duplicates: 0 Warnings: 0

mysql> select * from aa;
+--------+----------+-----+---------+
| 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 |
+--------+----------+-----+---------+
6 rows in set

mysql> desc aa;
+----------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| emp_id | int(11) | NO | | 0 | |
| emp_name | varchar(50) | YES | | NULL | |
| age | int(11) | YES | | NULL | |
| dept_id | int(11) | YES | | NULL | |
+----------+-------------+------+-----+---------+-------+
4 rows in set

#带EXISTS关键字的子查询（结果存在就返回true,不存在就返回false）
mysql> select * from employee where exists (select dept_name from department where dept_id=203);
+--------+----------+-----+---------+
| 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 |
+--------+----------+-----+---------+
6 rows in set

#不存在就返回false
mysql> select * from employee where exists (select dept_name from department where dept_id=205);
Empty set