mysql——多表——外連接查詢——左連接、右連接、復合條件查詢

create table employee ( num int(50),
                        d_id int(50),
                        name varchar(50),
                        age int(50),
                        sex varchar(50),
                        homeadd varchar(50)
                       );


insert into employee values(1,1001,'zhangsan',26,'nan','beijing');
insert into employee values(2,1001,'lisi',24,'nv','hunan');
insert into employee values(3,1002,'wangwu',25,'nan','jiangsu');
insert into employee values(4,1004,'aric',15,'nan','yingguo');


select * from employee;






create table department ( d_id int(50),
                          d_name varchar(50),
                          functione varchar(50),
                          address varchar(50)
                        );


insert into department values(1001,'keyanbu','yanfachanpin','3lou5hao');
insert into department values(1002,'shengchanbu','shengchanchanp','5louyiceng');
insert into department values(1003,'xiaoshoubu','cehuaxiaoshou','1louxiaoshoudating');



select * from department;






select num,name,employee.d_id,age,sex,d_name,functione from employee,department where employee.d_id = department.d_id;


內連接查詢：可以查詢兩個或者兩個以上的表，當兩個表中存在表示相同意義的字段時，可以通過該字段來連接這兩個表；

             當該字段的值相等時，就查詢出該記錄。

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外連接查詢：可以查詢兩個或者兩個以上的表，外連接查詢也需要通過指定字段來進行連。

            當該字段取值相等時，可以查詢出該記。

            而且該字段取值不相等的記錄也可以查詢出來。

外連接包括：左連接、右連接

語法：

        select 屬性列表 from 表名1 left | right join 表名2 on 表名1.屬性名1 = 表名2.屬性名2；

屬性列表表示要查詢的字段的名稱，這些字段可以來自不同的表；

Left表示左連接查詢；

rigth表示右連接查詢；

on后面接的是連接的條件；


1、左連接查詢

進行左連接查詢時，可以查詢出表名1所指的表中的所有記錄。而表名2所指的表中，只能查詢出匹配的記錄

select * from employee;
select * from department;

select num,name,employee.d_id,age,sex,d_name,functione from employee left join department on employee.d_id = department.d_id;


2、右連接查詢

進行右連接查詢時，可以查詢出表名2所指的表中的所有記錄。而表名1所指的表中，只能查詢出匹配的記錄

select * from employee;
select * from department;

select num,name,employee.d_id,age,sex,d_name,functione from employee right join department on employee.d_id = department.d_id;


復合條件查詢

在連接查詢時，通過增加其他的限制條件，可以使查詢結果更加准確

select * from employee;
select * from department;

select num,name,employee.d_id,age,sex,d_name,functione from employee,department where employee.d_id = department.d_id;

select num,name,employee.d_id,age,sex,d_name,functione from employee,department where employee.d_id = department.d_id and age > 24;

select num,name,employee.d_id,age,sex,d_name,functione from employee,department where employee.d_id = department.d_id order by age asc;

select 語句先按照內連接的方式從employee和department表中查詢出數據。然后查詢結果按照age字段從小到大的順序進行排序。

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前期准備表語句：

create table employee ( num int(50),
                        d_id int(50),
                        name varchar(50),
                        age int(50),
                        sex varchar(50),
                        homeadd varchar(50)
                       );


insert into employee values(1,1001,'zhangsan',26,'nan','beijing');
insert into employee values(2,1001,'lisi',24,'nv','hunan');
insert into employee values(3,1002,'wangwu',25,'nan','jiangsu');
insert into employee values(4,1004,'aric',15,'nan','yingguo');


select * from employee;





create table department ( d_id int(50),
                          d_name varchar(50),
                          functione varchar(50),
                          address varchar(50)
                        );


insert into department values(1001,'keyanbu','yanfachanpin','3lou5hao');
insert into department values(1002,'shengchanbu','shengchanchanp','5louyiceng');
insert into department values(1003,'xiaoshoubu','cehuaxiaoshou','1louxiaoshoudating');


select * from department;

select * from employee;

 

 select * from department;

 

 

左連接查詢：

語法：

select   屬性列表   from   表名1    left | right   join    表名2   on    表名1.屬性名1    =   表名2.屬性名2；

屬性列表表示要查詢的字段的名稱，這些字段可以來自不同的表；

Left表示左連接查詢；

rigth表示右連接查詢；

on后面接的是連接的條件；

1、左連接查詢

進行左連接查詢時，可以查詢出表名1所指的表中的所有記錄。而表名2所指的表中，只能查詢出匹配的記錄

select num,name,employee.d_id,age,sex,d_name,functione from employee left join department on employee.d_id = department.d_id;

 

 

 

 

 

2、右連接查詢

進行右連接查詢時，可以查詢出表名2所指的表中的所有記錄。而表名1所指的表中，只能查詢出匹配的記錄

select num,name,employee.d_id,age,sex,d_name,functione from employee right join department on employee.d_id = department.d_id;

 

 

 

 

 

 

3、復合條件查詢

在連接查詢時，通過增加其他的限制條件，可以使查詢結果更加准確

 

select num,name,employee.d_id,age,sex,d_name,functione from employee,department where employee.d_id = department.d_id;

select num,name,employee.d_id,age,sex,d_name,functione from employee,department where employee.d_id = department.d_id and age > 24;

select num,name,employee.d_id,age,sex,d_name,functione from employee,department where employee.d_id = department.d_id order by age asc;