如何包括查詢零計數結果

Question

我有這兩個表：

運營商：

Id Nome 
--+---- 
1 JDOE 
2 RROE 
3 MMOE 

電話：

Id CallDate OpId 
--+--------+---- 
1 20161228 2 
2 20161228 3 
3 20161228 2 
4 20161228 3 
5 20170104 1 
6 20170104 2 
7 20170104 1  

而這個查詢：

SELECT Operators.id, Operators.Nome, Count(Calls.OpId) AS CountCalls 
FROM Operators LEFT JOIN Calls ON Operators.id = Calls.OpId 
GROUP BY Calls.CallDate, Operators.id, Operators.Nome 
HAVING Calls.CallDate=20170104; 

其中返回：

Id Nome CountCalls 
--+----+---------- 
1 JDOE   2 
2 RROE   1 

我該如何讓它返回呢？

Id Nome CountCalls 
--+----+---------- 
1 JDOE   2 
2 RROE   1 
3 MMOE   0 

即，如何在任何查詢包括也由具有在左接合表中沒有發生，至少在由查詢過濾標準中定義的數據切片主表中的結果爲零？

PS。這是訪問2013

PS2。我讀過this answer，但看不出與我所做的有什麼不同，所以如果有人能在幫我複製我之前幫助我（也可能有相同的疑問），我將非常感激。

非常感謝！

Answer 1

因爲您在HAVING子句中提及Calls.CallDate，所以您將刪除沒有呼叫的運營商。如果沒有呼叫，則CallDate將是NULL，並且NULL=20170104不是真的，因此這些行被排除。你需要這個謂詞移動到連接語句：

SELECT Operators.id, Operators.Nome, Count(Calls.OpId) AS CountCalls 
FROM Operators LEFT JOIN Calls ON (Operators.id = Calls.OpId AND Calls.CallDate=20170104) 
GROUP BY Calls.CallDate, Operators.id, Operators.Nome; 

你也不必按Calls.CallDate，因爲你只有一個，所以你可以只使用：

SELECT Operators.id, Operators.Nome, Count(Calls.OpId) AS CountCalls 
FROM Operators LEFT JOIN Calls ON (Operators.id = Calls.OpId AND Calls.CallDate=20170104) 
GROUP BY Operators.id, Operators.Nome; 

由於一邊HAVING是錯誤的運算符。 HAVING是用於過濾聚集，因爲你沒有過濾的集合，你只需要使用WHERE

SELECT Operators.id, Operators.Nome, Count(Calls.OpId) AS CountCalls 
FROM Operators LEFT JOIN Calls ON Operators.id = Calls.OpId 
WHERE Calls.CallDate=20170104 
GROUP BY Calls.CallDate, Operators.id, Operators.Nome; 

你會使用HAVING如果你想郝曉紅上CountCalls，例如，如果你只是想操作符取得了超過1叫你可以使用：

SELECT Operators.id, Operators.Nome, Count(Calls.OpId) AS CountCalls 
FROM Operators LEFT JOIN Calls ON Operators.id = Calls.OpId 
WHERE Calls.CallDate=20170104 
GROUP BY Calls.CallDate, Operators.id, Operators.Nome 
HAVING Count(Calls.OpId) > 1; 

這隻會返回下面q

Id Nome CountCalls 
--+----+---------- 
1 JDOE   2 

Answer 2

嘗試uery：

SELECT o.id, o.name, count(c.opid) as countcalls 
FROM Operators o LEFT JOIN calls c ON o.id = c.opid AND c.calldate=20170104 
GROUP BY c.calldate, o.id, o.name 
ORDER BY o.id; 

輸出：

+------+------+------------+ 
| id | name | countcalls | 
+------+------+------------+ 
| 1 | JDOE |   2 | 
| 2 | RROE |   1 | 
| 3 | MMOE |   0 | 
+------+------+------------+