Oracle 11g:查询不返回任何内容时,默认为静态值 [英] Oracle 11g: Default to static value when query returns nothing
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问题描述
在Oracle 11g中工作时,当表中存在该输入值时,我需要选择一个与该输入值相对应的数据,而当输入值不存在时,则需要选择一个静态默认值.我能找到的最好的方法就是写这样的东西:
Working in Oracle 11g, I have a need to select a datum corresponding to an input value when that value exists in a table, and to instead select a static default value when it does not. The best way I could find to accomplish this was to write something like this:
SELECT desired_datum
FROM (
--Try to get explicit datum
SELECT desired_datum, 1 AS was_found
FROM data_table
WHERE the_key = &input_value
UNION
--Get default datum
SELECT 'default' AS desired_datum, 0 AS was_found
FROM dual
--Put explicit datum on top, if it exists
ORDER BY was_found DESC
) finder
WHERE ROWNUM <=1;
似乎必须有一些惯用的方式来执行此操作,而这并不依赖于ORDER BY
的这种奇怪用法,但是我找不到它.有谁知道更好的方法吗?
It seems like there must be some idiomatic way to do this which doesn't depend on this strange use of ORDER BY
, but I couldn't find it. Does anyone know of any better methods?
推荐答案
这应该是您所做的工作的简单版本:
This should be a simpler version of what you did:
SELECT NVL(desired_datum, 'default') AS desired_datum
FROM DUAL LEFT JOIN data_table ON the_key = &input_value
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