在查詢中使用多個表返回空值

Question

我是SQL新手，只知道基礎知識。如果有人能幫助下面的查詢，我將不勝感激。這將返回字段具有值的所有值，但是對於LO.Filurecode，需要返回該值時存在空值以及識別並填充缺失值。任何人都可以幫助看到下面的酷兒。

alter session set current_schema=maximo; 

select 
l.location, 
l.description, 
l.siteid, 
l.type, 
l.status, 
lh.parent, 
lo.failurecode, 
lo.locpriority, 
L.PLUSGSAFETYCRIT, 
L.PLUSGENVCRIT, 
L.PLUSGCOMCRIT, 
L.PLUSGEXREGISTERED, 
l.ta, 
l.taqamanufacturer, 
l.modelnum, 
l.PLUSGLOCREFERENCE, 
l.PLUSGPHYSLOC 
from 
locations l, lochierarchy lh, locoper lo 
where 
l.location = lh.location 
and l.location = lo.location 
and l.siteid = lo.siteid 
and l.siteid = lh.siteid 
and l.type ='OPERATING' 
and lh.systemid ='PRIMARY' 
and l.siteid ='COA' 
order by location 

Answer 1

這裏是有點重構您的查詢：

SELECT l.location, 
    l.description, 
    l.siteid, 
    l.type, 
    l.status, 
    lh.parent, 
    lo.failurecode, 
    lo.locpriority, 
    l.PLUSGSAFETYCRIT, 
    l.PLUSGENVCRIT, 
    l.PLUSGCOMCRIT, 
    l.PLUSGEXREGISTERED, 
    l.ta, 
    l.taqamanufacturer, 
    l.modelnum, 
    l.PLUSGLOCREFERENCE, 
    l.PLUSGPHYSLOC 
FROM locations l 
LEFT JOIN lochierarchy lh ON lh.location = l.location 
          AND lh.siteid = l.siteid 
          AND lh.systemid = 'PRIMARY' 
LEFT JOIN locoper lo ON lo.location = l.location 
         AND lo.siteid = l.siteid 
WHERE l.type ='OPERATING' 
and l.siteid ='COA' 
ORDER BY l.location 

我用明確的法定的繼承權語法（INNER JOIN, LEFT JOIN），而不是你所使用的舊學校語法。它更具可讀性，並且會更容易理解。

希望這會有所幫助。