本文介绍了Oracle 11g:当查询不返回任何内容时默认为静态值的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
在 Oracle 11g 中工作时，我需要选择一个与表中存在的输入值相对应的数据，而当该值存在于表中时，我需要选择一个静态默认值.我能找到的最好的方法是写这样的东西:
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法来做到这一点，它不依赖于 ORDER BY 的这种奇怪用法，但我找不到它.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
这应该是你所做的更简单的版本:
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
这篇关于Oracle 11g:当查询不返回任何内容时默认为静态值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持编程学习网！
本站部分内容来源互联网,如果有图片或者内容侵犯您的权益请联系我们删除！