Sql 如何连接两个表在不存在id为空的行上获得记录显示

我想要下面提到的预期结果。 下面是SQL查询：

+-------------------------------------------+
|              student Details              |
+-------------------------------------------+
|DetailsID(Idendtity)| StudentID| subjectID |
|      1             |  101     |    1001   |
|      2             |  101     |    1002   |   
+-------------------------------------------+

+-------------------------------------------+
|              Assign student               |
+-------------------------------------------+
|   AssingID         | StudentID| subjectID |
|      1             |  101     |    1001   |
|      1             |  101     |    1002   |   
+-------------------------------------------+

SELECT Distinct * FROM
   tbl_Studentdetails s LEFT OUTER JOIN  
   tbl_Assignstudent a ON s.studentID = a.studentID
   WHERE AssignId=1

实际结果：

SELECT Distinct * FROM
   tbl_Studentdetails s LEFT OUTER JOIN  
   tbl_Assignstudent a ON s.studentID = a.studentID
   WHERE AssignId=1

预期结果：

SELECT Distinct * FROM
   tbl_Studentdetails s LEFT OUTER JOIN  
   tbl_Assignstudent a ON s.studentID = a.studentID
   WHERE AssignId=1

+----------------------------------------+
| StudentID | subjectID | Exam 1 | Exam2 | 
|   101     |    1001   |  10:00 | 10:00 |
|   101     |    1002   |  01:00 | 02:00 |
+----------------------------------------+

---

WHERE

子句中的AssignId条件使

左连接

返回常规的

内部连接

结果。将条件移动到

ON

子句以获得true

LEFT JOIN

结果：

SELECT Distinct * FROM
   tbl_Studentdetails s LEFT OUTER JOIN  
   tbl_Assignstudent a ON s.studentID = a.studentID
   WHERE AssignId=1

+----------------------------------------+
| StudentID | subjectID | Exam 1 | Exam2 | 
|   101     |    1001   |  10:00 | 10:00 |
|   101     |    1002   |  01:00 | 02:00 |
|   101     |    1003   |  NULL  | NULL  |
+----------------------------------------+

---

没有

主题1003

。对于

Exam1、Exam2

列也是如此。他们从哪里来？对不起，我错过了学生表主体D最后一行的第一个表1003@asanraj . . . 不，没有。您应该编辑问题以显示实际数据。