Case語句和加入多個表的SQL問題

Question

下面是兩個表（請參閱SQLFiddle）的示例，我試圖創建select語句，其中一個表是查找（Facility），另一個是數據表（WOENTITY） ，我想選擇從查找中獲取facitityname，並且每當它找到facilityID的多個條目時，只是將文本寫爲'Multiple locations'，或者如果它找到null或零，然後寫'unknown'，否則只需寫入facilityname，我試圖做一個用單個條目替換多個計數的情況。任何幫助表示讚賞。

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下面是表看起來怎麼樣，表WOEntity截圖和表設施 Image showing the table schema and expected end result

我首先從WOEntity表，然後想多個位置ID的獲取計數創建一個選擇Case語句但無濟於事，這裏是草案代碼。

select e.WOID, count(e.ENTITYUID) as CNT, 
    (case 
      when e.ENTITYUID <> '0' and count(e.ENTITYUID) <=1 then 
       (Select FACILITYNAME from FACILITY l where e.ENTITYUID = 
        l.FACILITYID) 
      when count(e.ENTITYUID) > 2 then 'MULTIPLE FACILITIES' 
      else 'UNKNOWN LOCATIONS' 
    end) as facilityName 
From WOENTITY e 
group by e.WOID order by WOID; 

Answer 1

我會親自做了JOIN而不是相關子查詢，然後在CASE表達式使用COUNT：

SELECT e.WOID, 
     CASE WHEN COUNT(f.FACILITYID) = 0 THEN 'UNKNOWN LOCATIONS' 
      WHEN COUNT(f.FACILITYID) > 1 THEN 'MULTIPLE FACILITIES' 
      ELSE MAX(f.FACILITYNAME) 
     END AS facilityName 
FROM WOENTITY AS e 
     LEFT JOIN FACILITY AS f 
      ON f.FACILITYID = e.ENTITYUID 
GROUP BY e.WOID 
ORDER BY e.WOID; 

SQL Fiddle

既然你處理一個以上的，或零的情況下記錄與JOIN匹配，到達ELSE時，只有一條記錄，所以雖然使用MAX聚合函數，但只有一個輸入行，所以這沒有什麼作用，除了允許您選擇沒有gro的設施名稱由它提升。

編輯

我剛纔注意到，加拿大應顯示爲多個位置，即使只有其中一個存在於設備表，在這種情況下，你需要改變的情況下expresison咯，改變COUNT(f.FACILITYID)到COUNT(*)用於第二謂詞：

SELECT e.WOID, 
     CASE WHEN COUNT(f.FACILITYID) = 0 THEN 'UNKNOWN LOCATIONS' 
      WHEN COUNT(*) > 1 THEN 'MULTIPLE FACILITIES' 
      ELSE MAX(f.FACILITYNAME) 
     END AS facilityName 
FROM WOENTITY AS e 
     LEFT JOIN FACILITY AS f 
      ON f.FACILITYID = e.ENTITYUID 
GROUP BY e.WOID 
ORDER BY e.WOID; 

SQL Fiddle

Answer 2

的語句，你說你隨參數錯過了一個gorup ...財產以後這樣的：

select e.WOID, count(e.ENTITYUID) as CNT, 
    (case 
      when e.ENTITYUID <> '0' and count(e.ENTITYUID) <=1 then 
       (Select FACILITYNAME from FACILITY l where e.ENTITYUID = 
        l.FACILITYID) 
      when count(e.ENTITYUID) > 2 then 'MULTIPLE FACILITIES' 
      else 'UNKNOWN LOCATIONS' 
    end) as facilityName 
From WOENTITY e 
group by e.WOID,e.ENTITYUID order by WOID; 

Answer 3

這是考慮類似「加拿大

的情況下@GarethD答案的修改

SELECT e.WOID, 
     CASE WHEN COUNT(f.FACILITYID) = 0 THEN 'UNKNOWN LOCATIONS' 
      WHEN COUNT(f.FACILITYID) >0 and COUNT(coalesce(f.FACILITYID,'x'))>COUNT(f.FACILITYID) then 'MULTIPLE OFFICES' 
      WHEN COUNT(f.FACILITYID) > 1 then 'MULTIPLE OFFICES' 
      ELSE MAX(f.FACILITYNAME) 
     END AS facilityName 
FROM WOENTITY AS e 
     LEFT JOIN FACILITY AS f 
      ON f.FACILITYID = e.ENTITYUID 
GROUP BY e.WOID 
ORDER BY e.WOID; 

Answer 4

請試試這個

Select FACILITYID, 
    CASE WHEN (SELECT COUNT(*) 
       FROM WOEnTITY 
       WHERE WOEnTITY.ENTITYUID = FACILITYID) > 0 
     THEN 'MULTIPLE LOCATIONS' 
     ELSE '' 
    END 
FROM FACILITY 

Answer 5

您可以按照以下查詢：如下

Select Row_Number() over(order by Id) as Id, Woid, Case when FACILITYID is null then 'UNKNOWN LOCATIONS' 
       when RowCnt > 1 then 'MULTIPLE OFFICES' else FACILITYNAME end as FacilityName, 
       RowCnt as CountFacilities 
       from (
    Select *, RowCnt = count(EntityUid) over(partition by woid), 
    RowN = Row_Number() over(Partition by woid order by Id) 
    from WOENTITY we 
    left join Facility f 
    on we.ENTITYUID = f.FACILITYID 
) a 
Where a.RowN = 1 

輸出：

+----+---------+-------------------+-----------------+ 
| Id | Woid | FacilityName | CountFacilities | 
+----+---------+-------------------+-----------------+ 
| 1 | Canada | MULTIPLE OFFICES |    2 | 
| 2 | Germany | GREEN    |    1 | 
| 3 | India | GREEN    |    1 | 
| 4 | UK  | RED    |    1 | 
| 5 | US  | MULTIPLE OFFICES |    3 | 
| 6 | JAPAN | UNKNOWN LOCATIONS |    1 | 
+----+---------+-------------------+-----------------+