带案例的嵌套选择查询

Question

请查看查询。
我面临的问题是：
THEN 子句中的 FROM_LOCATION,TO_LOCATION 需要是 B_TARIFFS 中的值，但是当我在它前面加上 B_TARIFFS.FROM_LOCATION 和 B_TARIFFS.TO_LOCATION 时，我收到一个错误 @987654323 @。 如果它在ELSE 子句中可用，那么为什么我不能在THEN 子句中使用它。我该怎么做才能得到我想要的结果。
我想从查询中得到的结果是：Get from_location,to_location,关税（基于另一个表中的案例）。我期望外部查询将其 FROM_LOCATION,TO_LOCATION 传递给CASE ELSE THEN 中的内部选择查询，并基于此返回关税值，这将是外部查询的第三列。我能做些什么来实现这一目标。

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

你的问题在于双重嵌套。

你为什么不改变：

    (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) 

与

    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

正如@alexandergs 所述，错误的原因是子查询嵌套太深。但你有比这更大的问题。 在您的 when 子句中，您根据一些随机行做出决定，因为存在条件 rownum=1 没有排序。 else 子句中也是如此。也不清楚这个when (select ...) = '' 是什么意思 - 我怀疑你想显示一些不空的东西， 但目前的建设并没有提供这一点。您必须将查询重建为类似此处的内容：

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;

...最终为 row_number() 添加更多代码 - 因此它会根据您的需要对行进行排序并获取 RN = 1 的行。