Question

create table area (
area_id int(11) not null auto_increment,
area_name varchar(60) not null,
primary key (area_id)
);

create table mainCategory(
mc_id int(11) not null auto_increment,
mc_name varchar(60) not null,
area_id int(11) not null,
primary key(mc_id),
foreign key(area_id) references area(area_id)
);

create table subCategory(
sc_id int(11) not null auto_increment,
sc_name varchar(60) not null,
mc_id int(11) not null,
area_id int(11) not null,
primary key(sc_id),
foreign key(mc_id) references mc(mc_id),
foreign key(area_id) references area(area_id)
);


create table shopes(
s_id int(11) not null auto_increment,
s_name varchar(60) not null,
s_address varchar(120) not null,
s_work varchar(255) not null,
s_imagepath varchar(255) not null,
s_image varchar(255) not null,
area_id int(11) not null,
mc_id int(11) not null,
sc_id int(11) not null,
primary key(s_id),
foreign key(area_id) references area(area_id),
foreign key(mc_id) references mc(mc_id),
foreign key(sc_id) references sc(sc_id)
);

我想用mysql join从四个表中选择数据。我正在使用

select s_name,s_address,s_work,s_image,area_name,mc_name from shopes inner join area on area.area_id=shopes.area_id inner join mainCategory on mc.area_id=area.area_id;

这是一个三表连接，它没有给出适当的结果。它给出了重复的结果。

Answer 1

试试这个：

select s.s_name, s.s_address, s.s_work, s.s_image, a.area_name, mc.mc_name  from shope as s LEFT JOIN area as a on a.area_id=s.area_id LEFT JOIN mainCategory as mc on mc.area_id=a.area_id LEFT JOIN subCategory as sc on sc.area_id=a.area_id

我使用了LEFT JOIN关键字而不是内连接，它返回左表（table1）中的所有行，右表（table2）中的匹配行。当没有匹配时，结果在右侧为NULL。

Answer 2

使用此语法。

select a.coumn1, 
a.coumn2,
b.coumn1, 
c.coulumn1,
d.column1,
d.column2
from table1 a 
left outer join table2 b 
on a.id=b.id 
left outer join table3 c 
on b.id=c.id 
left outer join table4 d 
on a.id=d.id 
where a.name = 'abc'

Answer 3

select s_name, s_address, s_work, s_image, area_name, mc_name
from shopes, area, mainCategory
where shopes.area_id = area.area_id
and shopes.mc_id = mainCategory.mc_id;

如果仍有重复数据，请使用：

select distinct s_name, ...

Answer 4

select s_name,s_address,s_work,s_image,area_name,mc_name
  from area
 inner join area
    on area.area_id=shopes.area_id
 inner join mainCategory
    on mc.area_id=area.area_id;

Answer 5

试试吧。从shopes.area_id = area.area_id上的shopes join区域中选择shopes.s_name，s_address，s_work，s_image，area.area_name，maincategory.mc_name 在shopes.mc_id = maincategory.mc_id;

上加入maincategory

如何在msql中加入四个表？

5 个答案: