SQL查詢優化，一次查詢即可獲得結果

Question

通過下面兩個查詢，我每個月都不會遇到嚴重的致命事故。

如何在一個查詢中針對不同的事故類型優化並獲得結果？

SELECT 
     COUNT(ICT.ID)      NoOfAccident,    
     YEAR(ICT.[Date])   AccidentYear,
     Month(ICT.[Date])  AccidentMonth,
     MAX(ICT.[Date])  AS    AccidentDate
    FROM
    Accidents ICT   
        Where   
        ICT.AccidentType    = "Serious"
        AND 
        ICT.[Date] > CONVERT(DATETIME, '09/20/13', 1)
    Group By
    YEAR(ICT.[Date]),
    Month(ICT.[Date])
    ORDER BY
    IncidentDate ASC


SELECT 
 COUNT(ICT.ID)      NoOfAccident,    
 YEAR(ICT.[Date])   AccidentYear,
 Month(ICT.[Date])  AccidentMonth,
 MAX(ICT.[Date])  AS    AccidentDate
FROM
Accidents ICT   
    Where   
    ICT.AccidentType    = "Fatal"
    AND 
    ICT.[Date] > CONVERT(DATETIME, '09/20/13', 1)
Group By
YEAR(ICT.[Date]),
Month(ICT.[Date])
ORDER BY
IncidentDate ASC

我們如何在一個查詢中優化並獲得結果，例如：

NoOfSeriousAccident
NoOfFatalAccident
AccidentYear
AccidentMonth
AccidentDate 

Answer 1

平凡的-不僅按年份和月份分組，還按AccidentType分組（並刪除每個查詢一種accidedenttype的過濾器）。

這樣，您每年/每月將獲得2行-每種事故類型一次。

Answer 2

SELECT 
 ICT.AccidentType,
 COUNT(ICT.ID)      NoOfAccident,    
 YEAR(ICT.[Date])   AccidentYear,
 Month(ICT.[Date])  AccidentMonth,
 MAX(ICT.[Date])  AS    AccidentDate
FROM
Accidents ICT   
    Where   
    ICT.AccidentType IN ("Serious","Fatal")
    AND 
    ICT.[Date] > CONVERT(DATETIME, '09/20/13', 1)
Group By
ICT.AccidentType
YEAR(ICT.[Date]),
Month(ICT.[Date])
ORDER BY
IncidentDate ASC

編輯：根據更新的要求，您可以使用PIVOT來獲取致命和嚴重事故計數的單獨列，如下所示：

;with pivoted as
(select 
accidentyear, 
accidentmonth, 
serious as NoOfSeriousAccident, 
fatal as NoOfFatalAccident from
(SELECT 
 ICT.AccidentType,
 COUNT(ICT.ID)    cnt,
 YEAR(ICT.[accidentdate])   AccidentYear,
 Month(ICT.[accidentdate])  AccidentMonth
FROM
Accident ICT   
Where   
ICT.AccidentType IN ('Serious','Fatal')
AND 
ICT.[accidentdate] > CONVERT(DATETIME, '09/20/13', 1)
Group By
ICT.AccidentType,
YEAR(ICT.[accidentdate]),
Month(ICT.[accidentdate])) as s

pivot
(
max(cnt) 
for accidenttype in ([serious] ,[fatal])
) as pvt
)

select 
x.accidentyear, 
x.accidentmonth,
max(a.accidentdate), 
x.NoOfSeriousAccident, 
x.NoOfFatalAccident,
from pivoted x 
inner join accident a
on month(a.accidentdate) = x.accidentmonth
and year(a.accidentdate) = x.accidentyear
group by x.accidentmonth, x.accidentyear, x.seriouscount, x.fatalcount
order by max(a.accidentdate)

Answer 3

;WITH CTE AS (
SELECT 
     COUNT(ICT.ID)      NoOfAccident,    
     YEAR(ICT.[Date])   AccidentYear,
     Month(ICT.[Date])  AccidentMonth,
     MAX(ICT.[Date])  AS    AccidentDate,
     ICT.AccidentType As AccidentType

    FROM
    Accidents ICT   
        Where   
        ICT.AccidentType    = "Serious"
        AND 
        ICT.[Date] > CONVERT(DATETIME, '09/20/13', 1)
    Group By
    YEAR(ICT.[Date]),
    Month(ICT.[Date])
    ORDER BY
    IncidentDate ASC

UNION ALL
SELECT 
 COUNT(ICT.ID)      NoOfAccident,    
 YEAR(ICT.[Date])   AccidentYear,
 Month(ICT.[Date])  AccidentMonth,
 MAX(ICT.[Date])  AS    AccidentDate,
 ICT.AccidentType  As AccidentType
FROM
Accidents ICT   
    Where   
    ICT.AccidentType    = "Fatal"
    AND 
    ICT.[Date] > CONVERT(DATETIME, '09/20/13', 1)
Group By
YEAR(ICT.[Date]),
Month(ICT.[Date])
ORDER BY
IncidentDate ASC

)

select NoOfAccident,AccidentYear,AccidentMonth,AccidentDate,AccidentType  from CTE 
WHERE  AccidentType IN ('Fatal','Serious')