Question

我在下面有2张桌子

Paam Table
AssignmentID     PersonID         AssignmentType
300000014199240  300000014199145  E
300000014199174  300000014199145  ET

Par Table
ASGResponsID    AssignmentID    PersonID        Responsibility_Type
300000015244074 300000014199240 300000014199145 RC_HR_BP
300000015242351 300000014199240 300000014199145 RC_HR_BP
300000015244070 300000014199240 300000014199145 RC_HR_BP

我想加入这两个表并获得如下输出

PersonID         Responsiblity_Type
300000014199145  RC_HR_BP

我正在使用以下查询

select 
par.PersonID, par.Responsibility_Type 
from 
per_all_assignments_m paam, per_asg_responsibilities par
where
sysdate between nvl(paam.effective_start_date,sysdate) and 
nvl(paam.effective_end_date,sysdate)
and  paam.assignment_type='E'
and paam.assignment_id = par.assignment_id(+)
and paam.person_id = '300000014199145';

相反，我得到如下输出

PersonID         Responsiblity_Type
300000014199145  RC_HR_BP
300000014199145  RC_HR_BP
300000014199145  RC_HR_BP

尽管使用了左外部联接，但我得到了多行，为什么会这样？

有人可以帮我理解吗？

谢谢，湿婆

Answer 1

首先使用具有正确语法的常规join：

select par.PersonID, par.Responsibility_Type 
from per_all_assignments_m paam join
     per_asg_responsibilities par
     on paam.assignment_id = par.assignment_id and
        paam.person_id = par.person_id  -- presumably also needed for the join
where sysdate between nvl(paam.effective_start_date, sysdate) and 
nvl(paam.effective_end_date, sysdate) and
      paam.assignment_type = 'E' and
      paam.person_id = '300000014199145';

您对外部联接的意图可能是：

select par.PersonID, par.Responsibility_Type 
from per_asg_responsibilities par left join
     per_all_assignments_m paam
     on paam.assignment_id = par.assignment_id and
        paam.person_id = par.person_id  and
        sysdate between nvl(paam.effective_start_date, sysdate) and 
nvl(paam.effective_end_date, sysdate) and
        paam.assignment_type = 'E' and
where par.person_id = '300000014199145';

Answer 2

根据您的数据，您将获得正确的结果。 par表中的所有三行都具有相同的assignmentId（300000014199240），因此无论连接语法如何，查询都会返回该行。

添加“独特”子句将为您提供所需的结果。

select DISTINCT
  par.PersonID, par.Responsibility_Type 
from 
  per_all_assignments_m paam, per_asg_responsibilities par
where
  sysdate between nvl(paam.effective_start_date,sysdate) and 
  nvl(paam.effective_end_date,sysdate)
  and  paam.assignment_type='E'
  and paam.assignment_id = par.assignment_id(+)
  and paam.person_id = '300000014199145';

我在http://sqlfiddle.com/#!4/d7b7f/8的SQL小提琴中进行了设置。注意：我删除了日期字段引用，因为您没有为我们提供这些数据，但它不会根据您描述问题的方式影响结果。

尽管使用外部联接但仍存在多行

2 个答案: