SELECT w/ INNER JOIN 查詢可選列

我有五個表：File2、Branches_of_Study、Schools、Education_Establishments和Certificates。File2是事務表，所有其他表作為參考表。

File2都是關於員工的教育背景的。員工必須首先從站點的下拉列表中選擇教育機構，例如Highschool，College等。學習分支是指員工參加的課程，例如，，IT等。HRM``Photography

選擇後College，員工必須選擇一個Branch of Study。但是在選擇時Highschool，不允許選擇一個研究分支。

我在網站上有一個顯示所有員工教育程度的網格視圖。這是我的查詢：

SELECT File2.file2_id,
   File2.candidate_id,
   ee.education_establishment,
   s.school,
   File2.school_others,
   File2.start_date,
   File2.end_date,
   bs1.branch_of_study AS branch_of_study_1,
   c.certificate,
   File2.course_appraisal,
   bs2.branch_of_study AS branch_of_study_2
FROM File2
   INNER JOIN Education_Establishments ee
           ON File2.education_establishment_code = ee.education_establishment_code
   INNER JOIN Schools s
           ON File2.school_code = s.school_code
   INNER JOIN Branches_of_Study bs1
           ON File2.branch_of_study_1_code = bs1.branch_of_study_code
   INNER JOIN Branches_of_Study bs2
           ON File2.branch_of_study_2_code = bs2.branch_of_study_code
   INNER JOIN Certificates c
           ON File2.certificate_code = c.certificate_code
WHERE File2.candidate_id = 100003  

該查詢僅返回College員工編號條目的結果100003。我認為這是由條目欄位中null的值引起的。Branch of Study``Highschool

我想要一個查詢，它將顯示所有條目（College和Highschool），同時顯示參考表中的文本值（不是程式碼）。

如果連接是“可選的”，那麼根據定義，它不是內部連接。考慮調查左連接。

引用自：https://dba.stackexchange.com/questions/104136