mysql常用命令(二)
本片文章的重點是子查詢和左連線右連線，順便複習上一篇mysql常用命令(一)的一些命令。
建立之前判斷資料庫是否已經存在，COLLATE utf8_general_ci表示忽略大小寫
CREATE DATABASE IF NOT EXISTS testnewman DEFAULT CHARSET utf8 COLLATE utf8_general_ci;
建立student表
create table student(id int(11) NOT NULL AUTO_INCREMENT,
name varchar(20),
sex varchar(6),
submission_date date,
PRIMARY KEY (id)
)engine=innodb DEFAULT CHARSET=utf8;
插入資料
insert into student values(1,"小吳","男","2018-10-10");
insert into student values(2,"小張","女","2017-9-10");
insert into student values(3,"小李","女","2016-9-10");
insert into student values(4,"小程","男","2015-9-10");
查詢
select * from student;
select * from student where id =1;
select * from student where sex ='男';
select *from student where id in (2,4);
注意：只有2和4，不是2，3，4
select *from student where id not in (2,4);
起別名
select name as "男" from student where sex ='男';
只顯示第1個
select name as "男" from student where sex ='男' limit 1;
跳過第1個，顯示1個
select name as "男" from student where sex ='男' limit 1,1;
多個篩選條件
select name as "男" from student where sex ='男' and id =4;
select name as "男" from student where sex ='男' or id =4;
select name as "男" from student where submission_date >"2018-01-01";
select name as "男" from student where submission_date <>"2018-01-01";
分組聚合
select count(*),sex from student group by sex ;
select count(*),sex from student where id<3 group by sex ;
select count(*),sex from student where id>1 group by sex having count(*)=1;
建立id表
create table id(id int);
insert into id values(1);
insert into id values(2);
insert into id values(3);
insert into id values(4);
insert into id values(5);
select *from id;
子查詢
select * from student where id in (
select * from id where id>3);
建立A表
create table A(id int not null auto_increment,
name varchar(20) not null,
sex varchar(6),
salary varchar(20),
department_id int,
PRIMARY KEY (id)
)engine=innodb DEFAULT CHARSET=utf8;
create table department(
id int not null auto_increment,
department_name varchar(20) not null,
PRIMARY KEY (id)
)engine=innodb DEFAULT CHARSET=utf8;
向A表中插入資料
insert into A values(1,'jone','male',100,1);
insert into A values(2,'jane','female',60,2);
insert into A values(3,'jason','female',50,3);
insert into A values(4,"Jordan","male",20,10);
向department表中插入資料
insert into department values(1,"Hr");
insert into department values(2,"IT");
insert into department values(3,"OP");
insert into department values(4,"Finance");
內連線：不推薦使用，因為查詢速度會很慢
select person.name,depart.department_name from
A as person inner join department as depart on
person.department_id = depart.id;
或者
select person.name,depart.department_name from
A as person join department as depart on
person.department_id = depart.id;
左連線:列出左邊表中的所有內容，右邊表沒有想關聯的資料會顯示NULL
select person.name,depart.department_name from
A as person left join department as depart on
person.department_id = depart.id;
右連線:列出右邊表中的所有內容，左邊表沒有想關聯的資料會顯示NULL
select person.name,depart.department_name from
A as person right join department as depart on
person.department_id = depart.id;
找到兩個表中的所有欄位
select person.*,depart.* from
A as person right join department as depart on
person.department_id = depart.id;
union(合併排重的功能)
select id from A
union
select id from department;
union all(只合並)
select id from A
union all
select id from department;
select name from A
union all
select department_name from department;