Oracle查询3个带有2个外部连接的表格

Question

我在编写一个看起来应该很简单的查询时遇到了一些麻烦，但解决方案正在逃避我。

我们有三个表（简化这个问题的目的）： 者 - 用户名的表：

per_id  number(10) - primary key, populated by a sequence 
    user_name varchar2(50) 
    user_id  varchar2(15) - unique, basically the employee ID 

work_assignments - 有点像船员外派，但更普遍的：

wa_id  number(10) - primary key, populated by a sequence 
    wa_name varchar2(25) 

current_assignments - 哪些用户拥有哪些work_assignments;每用户平均大约为25的工作任务，但有些“幸运”的人有向上的150：

wa_id number(10) 
    per_id number(10) 

我想写一个查询，将比较work_assignments两个用户中，一共有三个列。结果应该是这样的：

WA_Name User_Name1 User_Name2 
Crew A Bob   Joe 
Crew B     Joe 
Crew C Bob 

基本上每个要么两个用户都有，与谁拥有它的用户（一个或多个）的姓名（或名称）work_assignment。

这是我能想出最接近的（当然，我也拿出来与3子查询，没有工作一个丑陋的查询，但是看起来应该有一个更优雅的解决方案）：

select distinct * from (
    select wa.name  work_assignment, 
     per.name  user_name1, 
     per2.name user_name2 
    from work_assignments wa join current_assignments ca on wa.wa_id = ca.wa_id 
           join current_assignments ca2 on wa.wa_id = ca2.wa_id 
        left outer join persons per on per.per_id = ca.per_id and per.user_id = 'X12345' 
        left outer join persons per2 on per2.per_id = ca2.per_id and per2.user_id = 'Y67890' 
        ) 
    where user_name1 is not null or user_name2 is not null 
    order by 1; 

这一个问题是，如果两个用户有一个工作任务，它显示了3个记录：一个是鲍勃，一个是乔，一个两个：

WA_Name User_Name1 User_Name2 
Crew A Bob   Joe 
Crew A     Joe 
Crew A Bob 

请帮帮忙！

感谢， 丹

Answer 1

我创建了一个样本数据集/表

drop table persons; 
drop table work_assgn; 
drop table curr_assgn; 


create table persons(
    per_id number(10) not null 
, user_name varchar2(10) not null 
, user_id varchar2(10) not null 
) 
; 

insert into persons values(1, 'Bob', 'X123'); 
insert into persons values(2, 'Joe', 'Y456'); 
insert into persons values(3, 'Mike', 'Z789'); 
insert into persons values(4, 'Jeff', 'J987'); 

commit; 

create table work_assgn(
    wa_id number(10) not null 
, wa_name varchar2(25) 
) 
; 

insert into work_assgn values(10, 'Crew A'); 
insert into work_assgn values(20, 'Crew B'); 
insert into work_assgn values(30, 'Crew C'); 
insert into work_assgn values(40, 'Crew D'); 

commit; 

create table curr_assgn(
    wa_id number(10) not null 
, per_id number(10) not null 
) 
; 

insert into curr_assgn values(10, 1); 
insert into curr_assgn values(10, 2); 
insert into curr_assgn values(20, 2); 
insert into curr_assgn values(30, 1); 
insert into curr_assgn values(40, 4); 

commit; 


select * from persons; 
select * from work_assgn; 
select * from curr_assgn; 

所以数据的模样

PERSONS 
    PER_ID USER_NAME USER_ID 
---------- ---------- ---------- 
     1 Bob  X123 
     2 Joe  Y456 
     3 Mike  Z789 
     4 Jeff  J987 


WORK_ASSGN 
    WA_ID WA_NAME 
---------- ------------------------- 
     10 Crew A 
     20 Crew B 
     30 Crew C 
     40 Crew D 

CURRASSGN 
    WA_ID  PER_ID 
---------- ---------- 
     10   1 
     10   2 
     20   2 
     30   1 
     40   4 

一种方法可以是使用PIVOT

with assignment as 
(
select p.user_id, p.user_name, a.wa_name 
from persons p 
join curr_assgn c 
    on p.per_id =c.per_id 
join work_assgn a 
    on a.wa_id = c.wa_id 
where p.user_id in ('X123', 'Y456') 
) 
select * from assignment 
pivot 
(max(user_name) for user_id in ('X123', 'Y456') 
) 
;