Oracle多对一（虚构表）

select * from user1
select * from dicts
-- 多对一（字典类应用）
drop table user1;
create table user1(
    id varchar2(10),
    username varchar2(20),
    sex varchar2(10),
    minzu varchar2(10)
);
insert into user1 values(1,'小明','男','汉族');
insert into user1 values(1,'小芳','女','傣族');
commit;
select * from user1

<option value="0">男</option>
<option value="1">女</option>
-----------------------------
drop table user1;
create table user1(
    id varchar2(10) primary key,
    user_name varchar2(20),
    sex number(1),
    minzu number(2)
);
insert into user1 values(1,'小明',1,1);
insert into user1 values(2,'小芳',0,2);
commit
select * from user1
drop table dicts
create table dicts(
   id number primary key,
   display varchar2(100), -- 显示内容
   key_value number,      -- 真实的值
   key_type varchar2(10),  -- 类别
   lang varchar2(10)      -- 语言
);

insert into dicts values(1,'男',1,'sex','cn');
insert into dicts values(2,'女',0,'sex','cn');
insert into dicts values(3,'boy',1,'sex','en');
insert into dicts values(4,'girl',0,'sex','en');
insert into dicts values(5,'汉族',1,'minzu','cn');
insert into dicts values(6,'傣族',2,'minzu','cn');
insert into dicts values(7,'hanzu',1,'minzu','en');
insert into dicts values(8,'daizu',2,'minzu','en');
select * from dicts

-- 传统的关联方式
select 
user1.id,
user_name,
dict_sex.display sex,--sex,
dict_minzu.display minzu--minzu
from user1,dicts dict_sex,dicts dict_minzu
where 
user1.sex=dict_sex.key_value and dict_sex.key_type='sex' and dict_sex.lang='en'
and
user1.minzu=dict_minzu.key_value and dict_minzu.key_type='minzu' and dict_minzu.lang='en'

-- 传统的关联方式2
select * from user1
select * from dicts where lang='cn' and key_type='sex'
select * from dicts where lang='cn' and key_type='minzu'

select user1.id,user_name,dict1.display sex,dict2.display minzu from 
user1,
(select * from dicts where lang='cn' and key_type='sex') dict1,
(select * from dicts where lang='cn' and key_type='minzu') dict2
where 
user1.sex=dict1.key_value
and
user1.minzu=dict2.key_value

-- 优化
select  user1.id,user_name,dict1.display sex,dict2.display minzu
from user1
left join 
(select * from dicts where lang='cn' and key_type='sex') dict1
on
user1.sex=dict1.key_value
left join 
(select * from dicts where lang='cn' and key_type='minzu') dict2
on
user1.minzu=dict2.key_value

-- 实验
select * from user1
insert into user1 values(4,'小红',2,1);
insert into user1 values(5,'小林',1,3);
commit

-- 观察内关联的结果
（小红和小林都丢了）
-- 观察左关联的结果


-- 继续对右表操作
select * from dicts
insert into dicts values(9,'外星族',99,'minzu','cn');
commit