SQL聯接查詢援助

Question

目前，我有2個疑問：

 
SELECT dateadd(month, x.MonthOffset,0) as [Month], SUM(x.itemcount) as [Total] FROM 
    (SELECT datediff(month,0, cna.impdate) as MonthOffset, count(*) as itemcount FROM myTable 
     WHERE (emergency = 'Emergency') AND (impdate BETWEEN '" + fromDate + "' AND '" + toDate + "') 
     GROUP BY impdate) x 
     GROUP BY MonthOffset ORDER BY MonthOffset asc 

SELECT dateadd(month, x.MonthOffset,0) as [Month], SUM(x.itemcount) as [Total] FROM 
    (SELECT datediff(month,0, cna.impdate) as MonthOffset, count(*) as itemcount FROM myTable 
     WHERE (impdate BETWEEN '" + fromDate + "' AND '" + toDate + "') 
     GROUP BY impdate) x 
     GROUP BY MonthOffset ORDER BY MonthOffset asc 

這將返回數據的2列與項目每月計數。

我的問題發生在存在一個月沒有緊急項目時。因爲我將對象傳遞給第二個查詢，如果從第一個檢索到的列數與第二個查詢不匹配，我將收到索引超出界限的錯誤。

如何將兩個查詢結合在一起，以便我可以有3列 - 月份，緊急總數和項目總數？緊急事件總數可以是0或null。

Answer 1

我沒有測試它的一種方式，但我認爲這應該給你你在找什麼：

SELECT dateadd(month, datediff(month,0, cna.impdate),0) as [Month], 
     count(*) as itemcount, 
     SUM(CASE WHEN emergency = 'Emergency' THEN 1 ELSE 0 END) AS EmergencyCount 
FROM myTable 
WHERE impdate BETWEEN '" + fromDate + "' AND '" + toDate + "' 
GROUP BY dateadd(month, datediff(month,0, cna.impdate),0) 
ORDER BY [Month] asc