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我有大约五个产生相同类型输出的查询，唯一的区别是它们从单独的表中获取数据，例如每小时表、每日表、每周表。

现在我想编写一个查询，它根据用户的输入从五个表之一生成输出。例如

IF THE USER PROVIDED TIMERANGE IS GREATER THAN 1 AND LESS THAN 24 HRS 
  THEN EXTRACT FROM HOURLY TABLE--i.e. execute 1st query 
IF THE USER PROVIDED TIMERANGE IS GREATER THAN 24 AND LESS THAN 7 DAYS
  THEN EXTRACT FROM DAILY TABLE-- i.e. execute 2nd query

......等等

注意：所有五个查询都返回相同类型的输出。也就是说，select 子句的投影对于所有查询都是相同的。

这可以通过单个 SQL 语句（可能使用联合）来完成，还是我需要为此编写一个 PL/SQL？

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2 回答 2

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您可以使用 UNION ALL 运算符执行此操作：

select * from hourly_table
where (&&user_end_date - &&user_start_day) < 1
union all
select * from weekly_table
where (&&user_end_date - &&user_start_day) between 1 and 7
union all
select * from monthly_table
where &&user_end_date <= add_months(&&user_start_day, 1)
union all
select * from yearly_table
where &&user_end_date <= add_months(&&user_start_day, 12)
union all
select * from whatever_table
where &&user_end_date > add_months(&&user_start_day, 12)

我对替换变量使用了 SQL*Plus 语法；您可能需要更改它以适合您用于运行查询的任何客户端。

于 2012-08-02T08:46:43.120 回答
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案例..什么时候可能有帮助

select 
CASE ConditionVar
  WHEN Val1 THEN Query1 
  WHEN Val2 THeN Query2
  ELSE QUERY3
END as myresult
from my_tables (dual in case no need of table);

案例详解 http://www.techonthenet.com/oracle/functions/case.php

替代语法，这在您的情况下可能更有用

select 
CASE 
   WHEN condition1 THEN Query1 
   WHEN condition2 THeN Query2
   ELSE QUERY3
END as myresult
from my_tables (dual in case no need of table);
于 2012-08-02T08:48:54.777 回答