与列值0显示记录时没有记录

Question

我有以下表：

架构

tbl_semester_empid {ID，semester_name VARCHAR（50），起始日期}

tbl_batch_empid {id，semester_id，batch_name，session_room}

tbl_associate_empid {id，associate_name，batch_id，contact，joining_date，induction_result，stream_result int}

问题查询是：显示学期明智的关联计数。

我已经写了3个查询：

--basic query 
SELECT s.ID "Semester Id", COUNT(*) "Associate Count" FROM TBL_SEMESTER_593932 s, TBL_ASSOCIATE_593932 a, TBL_BATCH_593932 b 
     WHERE s.ID=b.SEMESTER_ID AND a.BATCH_ID=b.ID 
       GROUP BY s.ID; 

--used NVL function 
SELECT s.ID "Semester Id", NVL(COUNT(*),0) "Associate Count" FROM TBL_SEMESTER_593932 s, TBL_ASSOCIATE_593932 a, TBL_BATCH_593932 b 
     WHERE s.ID=b.SEMESTER_ID AND a.BATCH_ID=b.ID 
       GROUP BY s.ID; 

-- used LEFT OUTER JOIN and JOIN 
SELECT s.ID "Semester Id", NVL(COUNT(*),0) "Associate Count" 
     FROM TBL_SEMESTER_593932 s LEFT OUTER JOIN TBL_BATCH_593932 b ON s.ID=b.SEMESTER_ID 
      JOIN TBL_ASSOCIATE_593932 a ON a.BATCH_ID=b.ID 
        GROUP BY s.ID; 

所有这些显示以下输出（其显示对应于仅在其至少1名学生，如果泰斯在那个学期没有学生的学期记录，不显示任何信息，这学期）：

我想在同事与他们没有任何关联的学期为0数列。所以，我想有两个LEFT OUTE同一连接：

SELECT s.ID "Semester Id", NVL(COUNT(*),0) "Associate Count" 
    FROM TBL_SEMESTER_593932 s LEFT OUTER JOIN TBL_BATCH_593932 b ON s.ID=b.SEMESTER_ID 
     LEFT OUTER JOIN TBL_ASSOCIATE_593932 a ON a.BATCH_ID=b.ID 
       GROUP BY s.ID; 

然而结果是怪异：

Answer 1

基本上，你必须做什么是使用所有可用的学期列表，然后计算每一个量：

select s.ID, 
     s.Semester_Name, 
     NVL ((select count(*) 
      from TBL_ASSOCIATE_593932 a 
       join TBL_BATCH_593932 b 
       on a.BATCH_ID=b.ID 
     where s.ID=b.SEMESTER_ID 
     ),0) as Amount 
from TBL_SEMESTER_593932 s 

另一种方法是左侧的接合部所有学期的名单再算上

select s.ID, 
     s.Semester_Name, 
     count(*) as Amount 
from TBL_SEMESTER_593932 s 
     left join (
      TBL_BATCH_593932 b 
      join TBL_ASSOCIATE_593932 a 
      on a.BATCH_ID=b.ID) 
      on s.ID=b.SEMESTER_ID 

group by s.ID, s.Semester_Name 
order by s.ID 

[编辑]：根据@ Mahesha999最后查询已得到纠正。

Answer 2

您是否尝试过使用CASE when？

根据您的关联表中的数据，也有所有批次/学期的记录。

那么试试这个，还有您的NVL类似情况......

select s.id, s.name, CASE WHEN count(a.id) IS NULL THEN 0 ELSE count(a.id) END as ACount 
from tblsem s 
left join tblbatch b 
on b.sid = s.id 
left join tblaso a 
on b.id = a.batchid 
group by s.id, s.name 
; 

结果：

ID NAME ACOUNT 
1 sem1 4 
2 sem2 3 
3 sem3 0 

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