如何包括查询零计数结果

Question

我有这两个表：

运营商：

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

电话：

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

而这个查询：

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 

我该如何让它返回呢？

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

即，如何在任何查询包括也由具有在左接合表中没有发生，至少在由查询过滤标准中定义的数据切片主表中的结果为零？

PS。这是访问2013

PS2。我读过this answer，但看不出与我所做的有什么不同，所以如果有人能在帮我复制我之前帮助我（也可能有相同的疑问），我将非常感激。

非常感谢！

Answer 1

因为您在HAVING子句中提及Calls.CallDate，所以您将删除没有呼叫的运营商。如果没有呼叫，则CallDate将是NULL，并且NULL=20170104不是真的，因此这些行被排除。你需要这个谓词移动到连接语句：

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，因为你只有一个，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; 

由于一边HAVING是错误的运算符。 HAVING是用于过滤聚集，因为你没有过滤的集合，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; 

你会使用HAVING如果你想郝晓红上CountCalls，例如，如果你只是想操作符取得了超过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; 

这只会返回下面q

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

Answer 2

尝试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; 

输出：

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