SQL Left Outer Join 的作用类似于 Inner Join答案

【问题标题】：SQL Left Outer Join acting like Inner JoinSQL Left Outer Join 的作用类似于 Inner Join
【发布时间】：2016-10-18 17:38:28
【问题描述】：

我正在尝试对两个表（嗯，一个内联视图和一个表）进行左外连接。我想要发生的是列出所有毕业生（我知道有 3815 名 DISTINCT 毕业生）以及他们的任何注册（可能有 0 或 n 个注册）。我得到的只是有注册的毕业生名单（3649 名 DISTINCT 学生）。我不确定我没有从 grad 'view' 中获取所有行（我没有 create view privs 所以这是我的解决方法）。

这是我的代码：

    SELECT C.*, D.FREEZE_EVENT, D.ACADEMIC_PERIOD, D.CAMPUS, D.COLLEGE, D.COLLEGE_DESC,D.MAJOR, D.MAJOR_DESC , D.STUDENT_RATE
FROM 
(SELECT A.STUDENT_LEVEL_DESC, A.CAMPUS, A.CAMPUS_DESC, A.COLLEGE, A.COLLEGE_DESC, A.MAJOR_DESC, A.MAJOR, A.DEGREE_DESC, A.PERSON_UID, A.ID, A.NAME, 
A.OUTCOME_GRADUATION_DATE, A.STATUS, A.GRAD_YEAR, A.TRAINING_LOCATION, B.CITIZENSHIP_TYPE
FROM ACAD_OUTOCME A, PERSON_DETAIL B
WHERE A.STUDENT_LEVEL IN ('02','03') AND A.GRAD_YEAR = '2015' AND A.FREEZE_EVENT = '10TH_SEP2016' AND B.FREEZE_EVENT = '10TH_SEP2016'
AND A.ID = B.ID) C 
LEFT OUTER JOIN ACAD_STUDY D ON
C.CAMPUS = D.CAMPUS 
AND C.COLLEGE = D.COLLEGE 
AND C.MAJOR = D.MAJOR
AND C.PERSON_UID = D.PERSON_UID
WHERE D.FREEZE_EVENT = '10TH_SEP2016' 
ORDER BY C.NAME

有什么建议吗？我正在使用 Toad 数据点。我也是工作中的贷款开发人员，所以我没有可以请任何人帮忙解决这个问题，而谷歌让我失望了。

谢谢！

【问题讨论】：

标签： sql left-join outer-join toad

【解决方案1】：

将WHERE 条件移动到ON 条件：

Select  C.*
      , D.FREEZE_EVENT
      , D.ACADEMIC_PERIOD
      , D.CAMPUS
      , D.COLLEGE
      , D.COLLEGE_DESC
      , D.MAJOR
      , D.MAJOR_DESC
      , D.STUDENT_RATE
From    (Select A.STUDENT_LEVEL_DESC
              , A.CAMPUS
              , A.CAMPUS_DESC
              , A.COLLEGE
              , A.COLLEGE_DESC
              , A.MAJOR_DESC
              , A.MAJOR
              , A.DEGREE_DESC
              , A.PERSON_UID
              , A.ID
              , A.NAME
              , A.OUTCOME_GRADUATION_DATE
              , A.STATUS
              , A.GRAD_YEAR
              , A.TRAINING_LOCATION
              , B.CITIZENSHIP_TYPE
         From   ACAD_OUTOCME A
         Join   PERSON_DETAIL B  On   A.ID = B.ID
         Where  A.STUDENT_LEVEL In ('02', '03')
                And A.GRAD_YEAR = '2015'
                And A.FREEZE_EVENT = '10TH_SEP2016'
                And B.FREEZE_EVENT = '10TH_SEP2016'
        ) C
Left Outer Join ACAD_STUDY D
        On C.CAMPUS = D.CAMPUS
           And C.COLLEGE = D.COLLEGE
           And C.MAJOR = D.MAJOR
           And C.PERSON_UID = D.PERSON_UID
           And D.FREEZE_EVENT = '10TH_SEP2016'
Order By C.NAME;

WHERE 子句在OUTER JOIN 之后评估，这将导致它从LEFT JOIN 中过滤掉NULL 记录。因此，在WHERE 子句中拥有LEFT JOIN 的右侧表格将有效地将OUTER JOIN 转换为INNER JOIN。

【讨论】：