帶案例的嵌套選擇查詢

Question

請看一下查詢。
我面臨的問題是：
THEN子句中的FROM_LOCATION ， TO_LOCATION必須是B_TARIFFS中的值，但是當我給它加上B_TARIFFS.FROM_LOCATION和B_TARIFFS.TO_LOCATION前綴時，會收到錯誤消息ORA-00904: Invalid identifier. 。 如果在ELSE子句中可用，那么為什么不能在THEN子句中使用它。 我該怎么做才能獲得理想的結果。
我從查詢中得到的結果是：獲取from_location，to_location，價目表（基於另一個表的情況）。 我期望外部查詢將其FROM_LOCATION，TO_LOCATION傳遞給CASE ELSE THEN的內部選擇查詢，基於此，將返回關稅價格，這將是外部查詢的第三列。 我該怎么做才能做到這一點。

select FROM_LOCATION, TO_LOCATION,

        case when (
            select  tariff A_tariff where A_tariff.FROM_LOCATION = B_TARIFFS.FROM_LOCATION AND A_tariff.TO_LOCATION = 
            B_TARIFFS.TO_LOCATION AND TO_DATE(sysdate,'YYYY-MM-DD')   between TO_DATE(from_date,'YYYY-MM-DD') and TO_DATE(to_date,'YYYY-MM-DD') 
            and rownum = 1
        ) = ''  
        then  

        (SELECT TARIFF FROM (
        SELECT * FROM A_TARIFF WHERE TRIM(A_TARIFF.FROM_LOCATION) = TRIM(**FROM_LOCATION**) AND 
        TRIM(A_TARIFF.TO_LOCATION) = TRIM(**TO_LOCATION**) ORDER BY A_TARIFF.FROM_DATE DESC 
        ) WHERE ROWNUM = 1) 

        else 

        (select  tariff from A_tariff where A_tariff.FROM_LOCATION = B_TARIFFS.FROM_LOCATION AND A_tariff.TO_LOCATION = 
        B_TARIFFS.TO_LOCATION AND TO_DATE(sysdate,'YYYY-MM-DD')   between TO_DATE(from_date,'YYYY-MM-DD') and TO_DATE(to_date,'YYYY-MM-DD') 
        and rownum = 1) end tariff

        FROM B_TARIFFS
        WHERE FROM_LOCATION LIKE '%ABC%' AND AREA_CODE = 'X' ORDER BY TARIFFS;

Answer 1

您的問題在於雙重嵌套。

你為什么不改變：

    (SELECT TARIFF FROM (
    SELECT * FROM A_TARIFF WHERE TRIM(A_TARIFF.FROM_LOCATION) = TRIM(**FROM_LOCATION**) AND 
    TRIM(A_TARIFF.TO_LOCATION) = TRIM(**TO_LOCATION**) ORDER BY A_TARIFF.FROM_DATE DESC 
    ) WHERE ROWNUM = 1) 

與

    SELECT TARIFF FROM A_TARIFF WHERE TRIM(A_TARIFF.FROM_LOCATION) = TRIM(B_TARIFFS.FROM_LOCATION) AND 
    TRIM(A_TARIFF.TO_LOCATION) = TRIM(B_TARIFFS.TO_LOCATION) WHERE ROWNUM = 1
    ORDER BY A_TARIFF.FROM_DATE DESC 

Answer 2

如@alexandergs所述，錯誤的原因是子查詢的嵌套太深。 但是，您所面臨的問題要大得多。 在您的when子句中，您會根據一些隨機行進行決策，因為存在條件rownum=1而不進行排序。 else子句中也是else 。 也不清楚when (select ...) = ''意味着什么-我懷疑您想顯示不為空的內容，但當前的構造方法無法提供此功能。 您必須將查詢重建為如下所示：

select b.from_location, b.to_location, a.tariff, b.tariffs, 
    row_number() over (partition by b.from_location, b.to_location 
                           order by a.from_date desc) rn
  from b_tariffs b
  left join a_tariff a 
         on a.from_location = b.from_location and a.to_location = b.to_location
         and trunc(sysdate) between trunc(a.from_date) and trunc(a.to_date) 
  where b.from_location like '%ABC%' and b.area_code = 'X' order by b.tariffs;

...最終為row_number（）添加更多代碼-因此它將根據您的需要對行進行排序，並采用RN = 1的行。