SQL生成多個計數列

Question

我開發了一些SQL來生成我們的本地故障單數據庫表（SQL Server 2008）的統計信息。從我的代碼中可以看到，我想從TICKETS中選擇，加入組以獲取組名稱，按組代碼以及年/月分組。

我想創建總計（計數）多少張門票是打開，關閉，在sla（過期日期）之外關閉的，最終是SLA％。

此代碼有效，但我不滿意編碼所有嵌套（選擇計數）;這似乎不是一個很好的策略與多次重新掃描。

是否有更好的設計來從桌面上的單個選擇生成多個「計數」列......或者這是標準方法嗎？

select g.group_name as [Group], 
     year(tm.date_open) as Year, 
     month(tm.date_open) as Month, 
     COUNT(*) as [Tickets Opened], 

     (select COUNT(*) 
     from TICKETS tm2 
     where tm2.group_code = tm.group_code 
     and year(tm2.COMPLETION_DATE) = year(tm.date_open) 
     and month(tm2.COMPLETION_DATE) = month(tm.date_open) 
     ) as [Tickets Closed], 

     (select COUNT(*) 
     from TICKETS tm2 
     where tm2.group_code = tm.group_code 
     and year(tm2.COMPLETION_DATE) = year(tm.date_open) 
     and month(tm2.COMPLETION_DATE) = month(tm.date_open) 
     and tm2.[COMPLETION_DATE] <= tm2.[DUE_DATE:] 
     ) as [Closed Within SLA], 

     (select COUNT(*) 
     from TICKETS tm2 
     where tm2.group_code = tm.group_code 
     and year(tm2.COMPLETION_DATE) = year(tm.date_open) 
     and month(tm2.COMPLETION_DATE) = month(tm.date_open) 
     and tm2.[COMPLETION_DATE] > tm2.[DUE_DATE:] 
     ) as [Closed Outside SLA] --service level agreement 


from TICKETS tm 
left join GROUPS g on g.group_code = tm.group_code 
where g.group_code in ('techs', 'reps', 'phone') 

and year(tm.date_open) = 2015 
--and month(tm.date_open) = 3 -- specific month 

group by tm.group_code, g.group_name, year(tm.date_open), month(tm.date_open) 

order by g.group_name, year(tm.date_open), month(tm.date_open) 

，我也要去想添加SLA％列將被（[關閉在SLA]/[關閉門票]）* 100。但是，當我看到它從我目前的設計，我會爲另一列添加冗餘嵌套SELECTS，例如...

(
    cast((select COUNT(*) 
    from TICKETS tm2 
    where tm2.group_code = tm.group_code 
    and year(tm2.COMPLETION_DATE) = year(tm.date_open) 
    and month(tm2.COMPLETION_DATE) = month(tm.date_open) 
    and tm2.[COMPLETION_DATE] <= tm2.[DUE_DATE:] 
    ) as decimal)/
    (select COUNT(*) 
    from TICKETS tm2 
    where tm2.group_code = tm.group_code 
    and year(tm2.COMPLETION_DATE) = year(tm.date_open) 
    and month(tm2.COMPLETION_DATE) = month(tm.date_open) 
    ) 
) * 100 as [SLA%] 

Answer 1

是的，你可以比一堆子查詢做得更好。在單個聚合查詢中，通過計算滿足條件時評估爲1的各種表達式，可以獲得滿足不同條件的單獨行數，否則爲零。或者，您可以使用COUNT()表達式計算出您想計算的那些行的非NULL。例如，它看起來像這樣可能接近你之後：

SELECT 
    g.group_name AS [Group], 
    year(tm.date_open) as Year, 
    month(tm.date_open) as Month, 
    COUNT(*) AS [Tickets Opened], 
    COUNT(tm.completion_date) AS [Tickets Closed], 
    SUM(CASE WHEN tm.completion_date <= [DUE_DATE:] THEN 1 ELSE 0 END) 
    AS [Closed Within SLA], 
    SUM(CASE WHEN tm.completion_date > [DUE_DATE:] THEN 1 ELSE 0 END) 
    AS [Closed Outside SLA], --service level agreement 
    CAST(SUM(CASE WHEN tm.completion_date <= [DUE_DATE:] THEN 1 ELSE 0 END) 
    AS decimal)/COUNT(tm.completion_date)) AS [SLA%], 
FROM 
    tickets tm 
    LEFT JOIN GROUPS g 
    ON g.group_code = tm.group_code 
WHERE 
    g.group_code in ('techs', 'reps', 'phone') 
    and year(tm.date_open) = 2015 
    -- and month(tm.date_open) = 3 -- specific month 
GROUP BY 
    tm.group_code, 
    g.group_name, 
    year(tm.date_open), 
    month(tm.date_open) 
ORDER BY 
    g.group_name, 
    year(tm.date_open), 
    month(tm.date_open)