create table 表名(
	列名1 数据类型1,
	列名2 数据类型2,
	....
	列名n 数据类型n
	);

insert into user2 values (1,'李四','123'); // 增
delete from pet where ower = 'disn'; //删
update pet set name = '后裔' where ower = 'dfn'; //改

①> 、< 、<= 、>= 、= 、<>	
②BETWEEN...AND	
③ IN( 集合)	
④LIKE 模糊查询	
⑤_单个任意字符
⑥%多个任意字符
⑦IS NULL 
⑧and 或 &&
⑨or 或 || 
⑩not 或 !
查询条件应用举例:
SELECT * FROM user WHERE age >= 18;
SELECT * FROM user WHERE age >= 18 AND age <=36;
SELECT * FROM user WHERE age BETWEEN 40 AND 70;
SELECT * FROM user WHERE age IN (6,18,37);
// 关于NULL
SELECT * FROM user WHERE height = NULL; 错误,因为null值不能使用=或（!=) 判断
SELECT * FROM user WHERE height IS NULL;(正确)
SELECT * FROM user WHERE height IS NOT NULL;(正确)
// 查询姓陈的有哪些？< like>
SELECT * FROM user WHERE NAME LIKE '陈%';
// 查询姓名第二个字是新的人
SELECT * FROM user WHERE NAME LIKE "_新%";
// 查询姓名是三个字的人
SELECT * FROM user WHERE NAME LIKE '___';
// 查询姓名中包含狗的人
SELECT * FROM user WHERE NAME LIKE '%狗%';

 create table user (
	id int primary key auto_increment, // 在创建表时，添加主键约束，并且完成主键自增	
	name varchar(20)
 );
-- 联合主键: 由多个字段联合组成的主键, 只要联合的主键加起来不重复就可以.联合主键中的任何一个字段都不能为空.
create table user2 (
 	id int,
 	name varchar(20),
 	password varchar(20),
 	primary key(id, name)
);

 create table user1 (
 	id int primary key auto_increment,
 	phone_num varchar(20) unique
 	 );
 create table user2 (
 	id int primary key auto_increment,
 	name varchar(20),
 	unique(id, name) // 表示两个字段在一起不重复就可以
 	 );
 	 

create table user3 (
	id int primary key auto_increment,
	name varchar(20) not null
	);

create table user4(
	id int primary key auto_increment,
	age int default 18,
	name varchar(20) not null
	);

create table 表名(
....
外键列
constraint 外键名称 foreign key (外键列名称) references 主表名称(主表列名称)
);
// 班级
create table classes(
	id int primary key,
	name varchar(20)
	);	
// 学生表
create table student (
		id	int primary key,
		name varchar(20),
		class_id int,
		foreign key(class_id) references classes(id)
		);
		

查询所有记录

例如:查询student表中的所有记录.

select * from student;

查询指定字段

例如:查询student中的sname,ssex,class.

select sname,ssex,class from student;

查询教师表中所有的单位即不重复的depart列. <排除重复distinct>

select distinct depart from teacher;

查询score表中成绩在60到80之间的所有记录 <查询区间 between…and…>

select * from score where degree between 60 and 80;
select * from score where degree > 60 and degree < 80;

查询score表中成绩为85,86或88的记录

select * from score where degree in(85, 86, 88);

查询student表中'95031'班或性别为'女'的同学记录. <or 表示或者>

select *from student where class = '95031' or sex = '女';

以class降序查询student表的所有记录 <降序:desc, 升序asc,默认升序(省略)>.

select * from student order by class desc;

以cno升序,degree降序查询score表的所有记录

select * from score order by cno asc,degree desc;

查询"95031'班的学生人数 <统计 count>

select count(*) from student where class = '95031';
查询score表中最高分的学生学号和课程号(子查询)

select sno, cno from score where degree = (select max(degree) from score );其中:select max(degree) from score 先查出最高分.

select sno,cno degree from score order by degree desc limit 0,1;其中:limit第一个数字表示从多少开始,第二个表示多少条.当有多个相同最高分时,容易出bug,不推荐使用这种方式查询.

查询每门课的平均成绩

select cno, avg(degree) from score group by cno;

查询score表中至少有2名学生选修的并以3开头的课程的平均分数.

select cno, avg(degree) from score group by cno having count(cno) >= 2 and cno like '3%';

查询分数大于70, 小于90的sno列.

select sno, degree from score where degree between 70 and 90;
查询所有学生的sname, cno和degree列.
select sname, cno, degree from student, score where student.sno = score.sno;
查询所有学生的sno,cname和degree列
select sno,cname,degree from course ,score where course.cno = score.cno;
查询"95031"班学生每门课的平均分.
select cno, avg(degree) from score where sno in (select sno from student where class = '95031') group by cno;
查询选修"3-105"课程的成绩高于"109"号同学"3-105"成绩的所有同学的记录.
select * from score where cno = '3-105' and degree > (select degree from score where sno = '109' and cno = '3-105');
查询成绩高于学号为"109", 课程号为"3-105"的成绩的所有记录
select * from score where degree > (select degree from score where sno = '109' and cno = '3-105');
查询和学号为108,101的同学同年出生的所有的sno, sname, sbirthday
select *from student where year(sbirthday) in (select year(sbirthday) from student where sno in(108, 101));
查询"张旭"教师任课的学生成绩
select * from score where cno = ( select cno from course where tno = (select tno from teacher where tname = "张旭"));
查询选修某课程的同学人数多于5人的教师姓名.
select tname from teacher where tno = (select tno from course where cno = (select cno from score group by cno having count(*) > 5));
查询存在有85分以上的成绩的课程的cno
select cno, degree from score where degree > 85;
查询出"计算机系"教师所教课程的成绩表
select * from score where cno in (select cno from course where tno in (select tno from teacher where depart = "计算机系"));
查询选修编号为"3-105"课程且成绩至少高于选休息编号为"3-245"的同学的cno,sno和degree,并按degree从高到低次序排序.
any 至少一个.

select * from score where cno = '3-105' and degree > any(select degree from score where cno = '3-245') order by degree desc;

select * from score where cno = '3-105' and degree > all(select degree from score where cno = '3-245') order by degree desc;

select * from score a where degree < (select avg(degree) from score b where a.cno = b.cno);
表a
+-----+-------+--------+
| sno | cno | degree |
+-----+-------+--------+
| 101 | 3-105 | 91 |
| 102 | 3-105 | 92 |
| 103 | 3-105 | 92 |
| 103 | 3-245 | 86 |
| 103 | 6-166 | 85 |
| 104 | 3-105 | 81 |
| 105 | 3-105 | 88 |
| 105 | 3-245 | 75 |
| 105 | 6-166 | 79 |
| 109 | 3-105 | 76 |
| 109 | 3-245 | 68 |
| 109 | 6-166 | 81 |
+-----+-------+--------+
12 rows in set (0.00 sec) 

表b
| sno | cno | degree |
+-----+-------+--------+
| 101 | 3-105 | 91 |
| 102 | 3-105 | 92 |
| 103 | 3-105 | 92 |
| 103 | 3-245 | 86 |
| 103 | 6-166 | 85 |
| 104 | 3-105 | 81 |
| 105 | 3-105 | 88 |
| 105 | 3-245 | 75 |
| 105 | 6-166 | 79 |
| 109 | 3-105 | 76 |
| 109 | 3-245 | 68 |
| 109 | 6-166 | 81 |
+-----+-------+--------+
12 rows in set (0.00 sec) 

分析用例的数据准备:
mysql> select * from person;
+----+--------+--------+
| id | name | cardId |
+----+--------+--------+
| 1 | 张三 | 1 |
| 2 | 李四 | 3 |
| 3 | 王五 | 6 |
+----+--------+--------+
3 rows in set (0.00 sec)
mysql> select * from card;
+------+-----------+
| id | name |
+------+-----------+
| 1 | 饭卡 |
| 2 | 建行卡 |
| 3 | 农行卡 |
| 4 | 工商卡 |
| 5 | 邮政卡 |
+------+-----------+
5 rows in set (0.00 sec)

select * from person inner join card on person.cardId = card.id;
+----+--------+--------+------+-----------+
| id | name | cardId | id | name |
+----+--------+--------+------+-----------+
| 1 | 张三 | 1 | 1 | 饭卡 |
| 2 | 李四 | 3 | 3 | 农行卡 |
+----+--------+--------+------+-----------+
2 rows in set (0.00 sec)

select * from person left join card on person.cardId = card.id;

+----+--------+--------+------+-----------+
| id | name | cardId | id | name |
+----+--------+--------+------+-----------+
| 1 | 张三 | 1 | 1 | 饭卡 |
| 2 | 李四 | 3 | 3 | 农行卡 |
| 3 | 王五 | 6 | NULL | NULL |
+----+--------+--------+------+-----------+
3 rows in set (0.00 sec)

select * from person right join card on person.cardId = card.id;

+------+--------+--------+------+-----------+
| id | name | cardId | id | name |
+------+--------+--------+------+-----------+
| 1 | 张三 | 1 | 1 | 饭卡 |
| 2 | 李四 | 3 | 3 | 农行卡 |
| NULL | NULL | NULL | 2 | 建行卡 |
| NULL | NULL | NULL | 4 | 工商卡 |
| NULL | NULL | NULL | 5 | 邮政卡 |
+------+--------+--------+------+-----------+
5 rows in set (0.01 sec)

mysql> select * from person full join card on person.cardId= card.id;
ERROR 1054 (42S22): Unknown column 'person.cardId' in 'on clause'
**** 解决mysql不支持full join的方法****
 <左连接 + 右链接> , 即通过union来连接左右连接. <左连接 union 右链接>.
eg:

select * from person left join card on person.cardId = card.id union select * from person right join card on person.cardId = card.id;

+------+--------+--------+------+-----------+
| id | name | cardId | id | name |
+------+--------+--------+------+-----------+
| 1 | 张三 | 1 | 1 | 饭卡 |
| 2 | 李四 | 3 | 3 | 农行卡 |
| 3 | 王五 | 6 | NULL | NULL |
| NULL | NULL | NULL | 2 | 建行卡 |
| NULL | NULL | NULL | 4 | 工商卡 |
| NULL | NULL | NULL | 5 | 邮政卡 |
+------+--------+--------+------+-----------+
6 rows in set (0.01 sec)

MYSQL执行语句顺序，严格遵循次顺序，不能改变
select
from
where
group by
having
order by

例如:
a --> -100
update user set money = money - 100 where name = 'a';
b --> +100
update user set money = money + 100 where name = 'b';
-- 实际程序中, 如果只有一条sql语句执行成功了,而另外一条没有执行成功?则会出现前后数据不一致的情况.
update user set money = money - 100 where name = 'a';
update user set money = money + 100 where name = 'b';
在多条sql语句,可能会有同时成功的要求,要么就同时失败.

mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
|  1 |
+--------------+
1 row in set (0.00 sec)
// 建表
create database bank;
create table user (
	id int primary key,
 name varchar(20),
 money int
 );
// 首先在表中插入一条用户数据a.
insert into user values (1,'a',1000);
Query OK, 1 row affected (0.00 sec)
// 进行回滚操作.
mysql> rollback;
Query OK, 0 rows affected (0.00 sec)
// 执行回滚后,查看数据表信息,发现即使调用了rollback,但插入的数据依然存在.说明当前不能回滚.
mysql> select * from user;
+----+------+-------+
| id | name | money |
+----+------+-------+
| 1 | a | 1000 |
+----+------+-------+
1 row in set (0.00 sec)
// 可以通过设置msql的回滚自动提交为false.
set autocommit = 0;
Query OK, 0 rows affected (0.00 sec)
mysql> select @@autocommit;
+--------------+
| @@autocommit |
+--------------+
|  0 |
+--------------+
1 row in set (0.00 sec)
// 也就说, 通过上面的set autocommit = 0;操作关闭了mysql的自动提交(commit).
*******再次插入数据:*******
insert into user values (2,'b',1000);
Query OK, 1 row affected (0.00 sec)
// 插入数据后查看表,用户2数据添加成功.
mysql> select * from user;
+----+------+-------+
| id | name | money |
+----+------+-------+
| 1 | a | 1000 |
| 2 | b | 1000 |
+----+------+-------+
2 rows in set (0.00 sec)
// 执行回滚操作.
mysql> rollback;
Query OK, 0 rows affected (0.00 sec)
// 回滚后再次查看表,发现刚才插入的数据已经被干掉了.
mysql> select * from user;
+----+------+-------+
| id | name | money |
+----+------+-------+
| 1 | a | 1000 |
+----+------+-------+
1 row in set (0.01 sec)
**** 对于这种场景,如果想让用户b数据成功提交, 可以通过commit;命令执行手动提交操作.手动提交后,如果想再次通过rollback来撤销,则是不可以的.也就是说,事务一旦提交,执行的sql语句就不可以再撤销,也就是说事务一旦提交数据就会持久的产生效果.

即:
 当前默认为自动提交模式,此时执行rollback无效.执行下面sql语句:
 start transaction;(或者begin;)
 update user set money = money - 100 where name = 'a';
 update user set money = money + 100 where name = 'b';
 执行完插入a,b用户数据后,再执行rollback,发现可以成功回滚事务.可以成功切换成手动开启事务的模式.若想使得插入的数据生效,也需要手动执行commit进行提交操作.
 事务开启之后,一旦commit提交,就不可以回滚,也就说,当前的这个事务在提交的时候就已经结束了.
 

mysql> select @@global.transaction_isolation;
+--------------------------------+
| @@global.transaction_isolation |
+--------------------------------+
| REPEATABLE-READ  |
+--------------------------------+
1 row in set (0.00 sec)

例如:
create table myorder(
		product_id int,
		customer_id int,
		product_name varchar(20),
		customer_name varchar(20),
		primary key(product_id, customer_id
	);
	当前表中, 除主键以外的其他列, 只依赖于主键的部分字段.则不满足第二范式,通常需要拆表.
create table myorder(
		order_id int primary key,
		product_id int,
		customer_id int
	);
create table product (
		id int primary key,
		name varchar(20)
	);
create table customer(
		id int primary key,
		name varchar(20)
		);
拆分成三个表后,满足第二范式.

create table student(
	sno varchar(20) primary key,
	sname varchar(20) not null,
	ssex varchar(20) not null,
	sbrithday datetime,
	class varchar(20)
	);

create table student(
	sno varchar(20) primary key,
	sname varchar(20) not null,
	ssex varchar(10) not null,
	sbirthday datetime,
	class varchar(20)
)

create table teacher(
	tno varchar(20) primary key,
	tname varchar(20) not null,
	tsex varchar(20) not null,
	tbirthday datetime,
	prof varchar(20) not null,
	depart varchar(20) not null
	);

create table course(
	cno varchar(20) primary key,
	cname varchar(20) not null,
	tno varchar(20) not null,
	foreign key(tno) references teacher(tno)
	);

create table score(
	sno varchar(20) not null,
	degree decimal,
	primary key (sno, cno),
	foreign key (sno) references student(sno),
	foreign key (cno) references course(cno)
	);

insert into student values ('101','曾华','男','1977-09-01','95033');
insert into student values ('102','匡明','男','1975-10-02','95031');
insert into student values ('103','王丽','女','1976-01-23','95033');
insert into student values ('104','李军','男','1976-02-20','95033');
insert into student values ('105','王芳','女','1975-02-10','95031');
insert into student values ('106','陆君','男','1974-06-03','95031');
insert into student values ('107','王尼玛','男','1976-02-20','95033');
insert into student values ('108','张全蛋','男','1975-02-10','95031');
insert into student values ('109','赵铁柱','男','1974-06-03','95031');

insert into teacher values ('804','李成','男','1958-12-02','副教授','计算机系');
insert into teacher values ('856','张旭','男','1969-03-12','讲师','电子工程系');
insert into teacher values ('825','王萍','女','1972-05-05','助教','计算机系');
insert into teacher values ('831','刘冰','女','1977-08-14','助教','电子工程系');

insert into course values ('3-105','计算机导论', '825');
insert into course values ('3-245','操作系统', '804');
insert into course values ('6-166','数字电路', '856');
insert into course values ('9-888','高等数学', '831');
 
insert into score values('103','3-245','86');
insert into score values('105','3-245','75');
insert into score values('109','3-245','68');
insert into score values('103','3-105','92');
insert into score values('105','3-105','88');
insert into score values('109','3-105','76');
insert into score values('103','3-105','64');
insert into score values('105','6-166','79');
insert into score values('109','6-166','81');


create table person(
	id int primary key auto_increment,
	name varchar(20),
	cardId int
);

create table card (
	id int,
	name varchar(20)
);

insert into card values (1,'饭卡');
insert into card values (2,'建行卡');
insert into card values (3,'农行卡');
insert into card values (4,'工商卡');
insert into card values (5,'邮政卡');

insert into person values (1,'张三',1);
insert into person values (2,'李四',3);
insert into person values (3,'王五',6);