MYSQL入门总结

创建数据库及创建表

create schema/database ttest(名字);	//创建数据库

create table ttest(建好的数据库名字).new_table(表名字)
(
a int not null,
b varchar(20) null,
c char (30) null,
primary key (a)); //这个主键要用括号括起来

1.show columns from score; 2.desc education.score;

desc是describe的缩写

也可以查看某一列的信息

desc score(表名) s_score(列名);

show columns from ttest.table1;		//查看建好的table1的表信息

查看table1中b列的信息

desc ttest.table1 b;

表插入列、删除列、修改列、删除表

插入一列d：



删除d列：



修改c列为varchar(123)

查找数据

select from where group by having order by 语句

select * from new_table order by name,id desc;
//从表中输出所有列，排序顺序为优先name升序(asc系统默认),若name一样则依照id降序(desc)

select id,name,sum(number) from new_table group by name;
//按name的不同分成不同的组，每组中都输出对应的id，name和该name对应的所有number的和

列表原有数据select结果

group by 后可以跟多个列，具体看这篇，讲的非常棒。

https://blog.csdn.net/u014717572/article/details/80687042

and且 or或

between A and B not between A and B 含义就是英文意思

字符串匹配 %任意字符串 _匹配一个字符

如：‘abcdefg’ like ‘%’ IS TRUE

‘abc’ like ‘a_c’ IS TRUE

聚合函数：count()计算选定集合中选定列的非NULL值的数目

max() min() 计算集合中选定列中最大最小值

sum() 选定列求和

avg() 选定列求平均值

连接查询

education数据库，包含四个表 课程、成绩、学生信息、教师信息

建数据库代码如下：

CREATE TABLE `Student`(
    `s_id` VARCHAR(20),
    `s_name` VARCHAR(20) NOT NULL DEFAULT '',
    `s_birth` VARCHAR(20) NOT NULL DEFAULT '',
    `s_sex` VARCHAR(10) NOT NULL DEFAULT '',
    PRIMARY KEY(`s_id`)
);
CREATE TABLE `Course`(
    `c_id`  VARCHAR(20),
    `c_name` VARCHAR(20) NOT NULL DEFAULT '',
    `t_id` VARCHAR(20) NOT NULL,
    PRIMARY KEY(`c_id`)
);
CREATE TABLE `Teacher`(
    `t_id` VARCHAR(20),
    `t_name` VARCHAR(20) NOT NULL DEFAULT '',
    PRIMARY KEY(`t_id`)
);
CREATE TABLE `Score`(
    `s_id` VARCHAR(20),
    `c_id`  VARCHAR(20),
    `s_score` INT(3),
    PRIMARY KEY(`s_id`,`c_id`)
);
insert into Student values('01' , '赵雷' , '1990-01-01' , '男');
insert into Student values('02' , '钱电' , '1990-12-21' , '男');
insert into Student values('03' , '孙风' , '1990-05-20' , '男');
insert into Student values('04' , '李云' , '1990-08-06' , '男');
insert into Student values('05' , '周梅' , '1991-12-01' , '女');
insert into Student values('06' , '吴兰' , '1992-03-01' , '女');
insert into Student values('07' , '郑竹' , '1989-07-01' , '女');
insert into Student values('08' , '王菊' , '1990-01-20' , '女');
insert into Course values('01' , '语文' , '02');
insert into Course values('02' , '数学' , '01');
insert into Course values('03' , '英语' , '03');
insert into Teacher values('01' , '张三');
insert into Teacher values('02' , '李四');
insert into Teacher values('03' , '王五');
insert into Score values('01' , '01' , 80);
insert into Score values('01' , '02' , 90);
insert into Score values('01' , '03' , 99);
insert into Score values('02' , '01' , 70);
insert into Score values('02' , '02' , 60);
insert into Score values('02' , '03' , 80);
insert into Score values('03' , '01' , 80);
insert into Score values('03' , '02' , 80);
insert into Score values('03' , '03' , 80);
insert into Score values('04' , '01' , 50);
insert into Score values('04' , '02' , 30);
insert into Score values('04' , '03' , 20);
insert into Score values('05' , '01' , 76);
insert into Score values('05' , '02' , 87);
insert into Score values('06' , '01' , 31);
insert into Score values('06' , '03' , 34);
insert into Score values('07' , '02' , 89);
insert into Score values('07' , '03' , 98);

内连接：

A inner join B

select *
from student inner join score
on student.s_id = score.s_id;		//on表示条件

运行：

外连接：

left join：

左侧表全部输出，同时输出右侧表满足 on后的条件 的值，不满足则输出null

select *
from student left join score
on student.s_id=score.s_id;	//用on表示条件

right join：

与left join相反

full join

全连接 返回左右表全部行，full join可以不跟on，此情况下等同于下面的交叉连接

交叉连接（笛卡尔积）

select count(*)
from student, score;	//返回144

select count(*)
from student cross join score; 	//返回144

子查询

带in的子查询

in 或not in

//输出姓赵的同学的成绩
select * from score
where s_id in (select s_id from student where s_name like '赵%');

带exists的子查询

exists或not exists

select * from score;
select * from score
where exists (select s_id from student where s_name like '赵%');

运行结果：



上面两个语句都返回score的全部信息，即下面的exists子查询未起到筛选作用

改进：

select * from score
where exists (select s_sex from student where s_name like '赵%' and student.s_id=score.s_id);

运行结果：

筛选成功



那么思考一下，exists其实只是一个存在量词的作用，即若exists后面跟的语句若返回一个非空集合则继续与前面比较，返回空集则不再继续比较。注意上面代码中exists后面select的是s_sex，但最终运行结果正确，即这里select的是什么不重要，再改成s_birth运行依然正确。

可以参考这里：

http://www.cnblogs.com/V1haoge/p/6385312.html

带any的子查询

any表示随便一个,比如 > any(select …),表示大于括号集合中任意一个值即可，不要与any的英文释义弄混了。

带all的子查询

all与any对应,表示后面集合中全部一个不漏都得怎么怎么样才行

select student.*,c_id,s_score
 from student left join score
 on student.s_id=score.s_id
 where s_score > all (select s_score from score where s_id=04);

运行结果：

多表查询

粘贴的，记录一下

本文链接：https://blog.csdn.net/adingyb/article/details/81234980

t2和t3数据表中存有他t1表中数据的id

选择删除t1表中的数据以及t2和t3表中相关（task_id）的数据

SQL语句如下：

DELETE t1,t2,t3 from cl_delivery_task t1

LEFT JOIN xh_saleact t2 ON t1.id=t2.task_id

LEFT JOIN xh_sale_detail t3 ON t1.id=t3.task_id

WHERE t1.id=‘2c27ec183faa4706ba3843c8238ced21’