SQL CASE對無數據的聲明

Question

我有一個具有運行狀態的流程引擎1,2,3,4,5,6的表。當其中一個引擎停機時，記錄將從表中刪除。使用case語句，我可以顯示停機的第一個引擎，但是如果有兩個或更多個引擎停機，我該如何去顯示引擎。對於例如如何使這個查詢顯示PE 2 IS DOWN，並且如果兩個引擎都關閉，PE 4將DOWN。現在它只顯示列表中第一個關閉的引擎。

SELECT CASE 
WHEN (SELECT COUNT(PE_ID) FROM CWVMINFO WHERE PE_ID = 1) = 0 THEN 'PE 1 IS DOWN' 
WHEN (SELECT COUNT(PE_ID) FROM CWVMINFO WHERE PE_ID = 2) = 0 THEN 'PE 2 IS DOWN' 
WHEN (SELECT COUNT(PE_ID) FROM CWVMINFO WHERE PE_ID = 3) = 0 THEN 'PE 3 IS DOWN' 
WHEN (SELECT COUNT(PE_ID) FROM CWVMINFO WHERE PE_ID = 4) = 0 THEN 'PE 4 IS DOWN' 
WHEN (SELECT COUNT(PE_ID) FROM CWVMINFO WHERE PE_ID = 5) = 0 THEN 'PE 5 IS DOWN' 
WHEN (SELECT COUNT(PE_ID) FROM CWVMINFO WHERE PE_ID = 6) = 0 THEN 'PE 6 IS DOWN' 
ELSE 'ALL PROCESS ENGINES ARE UP AND RUNNING' 
END "STATUS" 
from dual; 

Answer 1

相反情況下，使用union all了兩種不同的情況，所有的好與一些沒有運行。子查詢分解以減少重複代碼。

with engines as (select level as engine_number 
    from dual 
    connect by level <= 6) 
, down_engines as (select engine_number 
    from engines 
    where engine_number not in (select pe_id from cwvminfo)) 
select to_char(engine_number) || ' IS DOWN' 
from down_engines 
union all 
select 'all engines are running' 
from dual 
where not exists (select null from down_engines) 

Answer 2

您可以使用多個CASE表達式爲每個返回狀態：

WITH cte AS (
SELECT CASE WHEN (SELECT COUNT(PE_ID) FROM CWVMINFO WHERE PE_ID = 1) = 0 THEN 'PE 1 IS DOWN' END AS PE_1 
     ,CASE WHEN (SELECT COUNT(PE_ID) FROM CWVMINFO WHERE PE_ID = 2) = 0 THEN 'PE 2 IS DOWN' END AS PE_2 
     ,CASE WHEN (SELECT COUNT(PE_ID) FROM CWVMINFO WHERE PE_ID = 3) = 0 THEN 'PE 3 IS DOWN' END AS PE_3 
     ,CASE WHEN (SELECT COUNT(PE_ID) FROM CWVMINFO WHERE PE_ID = 4) = 0 THEN 'PE 4 IS DOWN' END AS PE_4 
     ,CASE WHEN (SELECT COUNT(PE_ID) FROM CWVMINFO WHERE PE_ID = 5) = 0 THEN 'PE 5 IS DOWN' END AS PE_5 
     ,CASE WHEN (SELECT COUNT(PE_ID) FROM CWVMINFO WHERE PE_ID = 6) = 0 THEN 'PE 6 IS DOWN' END AS PE_6 
     from dual) 
SELECT *,CASE WHEN COALESCE(PE_1,PE_2,PE_3,PE_4,PE_5,PE_6) IS NULL THEN 'ALL PROCESS ENGINES ARE UP AND RUNNING' END "STATUS" 
FROM cte 

Answer 3

我會寫一個存儲過程，如果條件爲每個在這裏的情況。

Answer 4

您可以嘗試以下操作。這有點笨拙，但我認爲它可能工作。

WITH p1 AS (
    SELECT LEVEL AS pe_id 
     FROM dual 
    CONNECT BY LEVEL <= 6 
) 
SELECT DISTINCT CASE WHEN all_ind = 0 THEN 'ALL PROCESS ENGINES ARE UP AND RUNNING' 
    WHEN process_cnt = 0 THEN 'PE ' || pe_id || ' IS DOWN' END AS status 
    FROM (
    SELECT pe_id, process_cnt 
     , SUM(DECODE(process_cnt, 0, 1, 0)) OVER () AS all_ind 
     FROM (
     SELECT p1.pe_id, COUNT(c1.pe_id) AS process_cnt 
      FROM p1 LEFT JOIN cwvminfo c1 
      ON p1.pe_id = c1.pe_id 
     GROUP BY p1.pe_id 
    ) 
) 

Please see SQL Fiddle here.

Answer 5

我想這個使用單個查詢和有條件的聚集改寫：

select coalesce(case when sum(case when pe_id = 1 then 1 else 0 end) = 0 
        then 'PE 1 IS DOWN; ' 
       end) || 
       (case when sum(case when pe_id = 1 then 2 else 0 end) = 0 
        then 'PE 2 IS DOWN; ' 
       end) || 
       (case when sum(case when pe_id = 1 then 3 else 0 end) = 0 
        then 'PE 3 IS DOWN; ' 
       end) || 
       (case when sum(case when pe_id = 1 then 4 else 0 end) = 0 
        then 'PE 4 IS DOWN; ' 
       end) || 
       (case when sum(case when pe_id = 1 then 5 else 0 end) = 0 
        then 'PE 5 IS DOWN; ' 
       end) || 
       (case when sum(case when pe_id = 1 then 6 else 0 end) = 0 
        then 'PE 6 IS DOWN; ' 
       end), 'ALL PROCESS ENGINES ARE UP AND RUNNING') as status 
from CWVMINFO; 

，或者，如果你沒有有單排，你可以這樣做：

select ids.id, 
     (case when count(c.pe_id) = 0 then "DOWN' else 'UP' end) as status 
from (select 1 as id from dual union all select 2 from dual union all select 3 from dual union all 
     select 4 union all select 5 union all select 6 from dual 
    ) ids left join 
    CWVMINFO c 
    on c.pe_id = ids.id 
group by ids.id 
order by ids.id; 

這會讓所有東西都被檢查更明顯。