SQL查詢返回一個結果，不返回0或NULL結果

Question

我試圖讓查詢列出顧問並提供每個活動學生的數量。我可以列出有1位學生的顧問，排除1位以上的顧問，但無法讓顧問返回0或NULL計數。

Select Advisors.AdvisorID, Advisors.FirstName, Advisors.LastName, COUNT(case Students.IsActive WHEN '1' then 1 else NULL end) AS "Number of Students" 
FROM Advisors, Students 
WHERE Advisors.AdvisorID=Students.AdvisorID 
GROUP BY Advisors.AdvisorID, Advisors.FirstName, Advisors.LastName 
HAVING COUNT(case Students.IsActive WHEN '1' then 1 else NULL end)='1' 

統計活動調查問卷，並返回顧問列表與顧問一個學生，與0學生顧問回來空白。我錯過了什麼？

Select Advisors.AdvisorID, Advisors.FirstName, Advisors.LastName, COUNT(case Students.IsActive WHEN '1' then 1 else NULL end) AS "Number of Students" 
FROM Advisors, Students 
WHERE Advisors.AdvisorID=Students.AdvisorID 
GROUP BY Advisors.AdvisorID, Advisors.FirstName, Advisors.LastName 
HAVING COUNT(case Students.IsActive WHEN '1' then 1 else NULL end) IS NULL 

回來與列名和任何數據。我有雙重檢查表顧問表有3個條目，一個有2個活躍的學生和一個非活動0或1使用位，一個沒有學生，一個有一個。

使用< = 1或< 1類似地導致空白數據。

Answer 1

請使用ANSI JOIN語法

Select Advisors.AdvisorID, 
      Advisors.FirstName, 
      Advisors.LastName, 
      COUNT(case Students.IsActive WHEN '1' then 1 else NULL end) AS "Number of Active Students" 
FROM  Advisors 
LEFT JOIN Students 
ON  Advisors.AdvisorID=Students.AdvisorID 
GROUP BY Advisors.AdvisorID, 
      Advisors.FirstName, 
      Advisors.LastName 
HAVING COUNT (Students.AdvisorID) = 1