IF中的多个选择语句

Question

我可以使用一些帮助为报告编写prog./sql构造..

Sql应首先检查提示＆amp;然后决定应该运行哪些“选择”语句

类似（伪代码）

Select ACCT,LOC FROM (

   IF :loc = 'MN' THEN
      Select acc as ACCT,location as LOC
   ELSE IF :loc = 'MA' THEN
      Select accid as ACCT,locid as LOC
   ELSE IF :loc = 'PA' THEN 
      Select accountid as ACCT,location as LOC
   END IF)

以上似乎不起作用。请帮忙！

Answer 1

你可以这样做：

Select acc as ACCT,location as LOC 
where :loc = 'MN' 
UNION ALL
Select accid as ACCT,locid as LOC 
where :loc = 'MA' 
UNION ALL
Select accountid as ACCT,location as LOC 
where :loc = 'PA';

Answer 2

怎么样......

select acc,
       case :loc
       When 'MN' then location
       When 'MA' then locid
       When 'PA' then location
       ...
       end
from   ...

或......

select acc,
       case when :loc in ('MN','PA')
            then location
            When :loc in ('MA',...)
            then locid
            ...
       end
from   ...

这样做会更友好，因为它会减少唯一游标的数量。

Answer 3

如果您可以创建自定义PL / SQL函数，那么您可以从中返回结果集（所谓的记录表），然后只从函数中选择。请参阅this article。