Where子句不在SQL Server CE中选择o count

Question

我在使用SQL CE选择所有计数值列表到表时遇到问题。

SELECT  Time AS Hour,Cast (COUNT(ReceivedTime)*1.0/(10)as decimal(16,2)) AS HourlyTotal 
    FROM tblTime 
    LEFT OUTER JOIN tblMessageReceived ON Time = ReceivedTime  
    WHERE ReceivedDateTime >= '2016-01-01'  AND ReceivedDateTime <= '2016-07-07' 
    GROUP BY Time

但它只选择非零计数。作为下面的结果表。

在这里，我想用0计数值选择所有小时时间。

Answer 1

您的WHERE条款有效地将您的LEFT JOIN变为INNER JOIN。解决方案是将它们放在ON子句中：

SELECT  
    t.Time AS Hour,
    CAST(COUNT(t.ReceivedTime)*1.0/(10) AS DECIMAL(16, 2)) AS HourlyTotal 
FROM tblTime t
LEFT OUTER JOIN tblMessageReceived tmr
    ON t.Time = tmr.ReceivedTime  
    AND tmr.ReceivedDateTime >= '2016-01-01'
    AND tmr.ReceivedDateTime <= '2016-07-07' 
GROUP BY t.Time

注意：

• 使用有意义的别名来提高可读性。