SQL/MySQL NOT NULL 与 NOT EMPTY
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SQL/MySQL NOT NULL vs NOT EMPTY
提问by cream
I'd like to limit my query to show only rows where a certain field is not empty. I found this threadwhere someone posed the same question and was told to use IS NOT NULL. I tried that, but I'm still getting rows where the field is empty.
我想将我的查询限制为仅显示某个字段不为空的行。我发现这个线程如果有人提出同样的问题，被告知使用IS NOT NULL。我试过了，但我仍然得到字段为空的行。
What is the correct way to do this? Is Null the same thing as Empty in SQL/MySQL?
这样做的正确方法是什么？Null 与 SQL/MySQL 中的 Empty 是否相同？
My query, if you're interested is:
SELECT * FROM records WHERE (party_zip='49080' OR party_zip='49078' OR party_zip='49284' ) AND partyfn IS NOT NULL
我的查询，如果你有兴趣是：
SELECT * FROM records WHERE (party_zip='49080' OR party_zip='49078' OR party_zip='49284' ) AND partyfn IS NOT NULL
采纳答案by Robin Castlin
When comparing a NULLvalue, the result in most cases becomes NULLand therefor haves the same result as 0(the FALSE value in MySQL) inside WHEREand HAVING.
当比较一个NULL值，结果在大多数情况下变得NULL和为此富人相同的结果0的内部（在MySQL的FALSE值）WHERE和HAVING。
In your given example, you don't need to include IS NOT NULL. Instead simply use party_zip IN ('49080', '49078', '49284'). NULLcan't be 49080, 49078, 49284 or any other number or string.
在您给定的示例中，您不需要包含IS NOT NULL. 而是简单地使用party_zip IN ('49080', '49078', '49284'). NULL不能是 49080、49078、49284 或任何其他数字或字符串。
What you do need to think about though, is when checking for empty values. !party_zipwon't return TRUE/1if the value is NULL. Instead use OR columns IS NULLor !COALESCE(party_zip, 0)
但是，您需要考虑的是检查空值时。如果值为 ，则!party_zip不会返回TRUE/ 。而是使用或1NULLOR columns IS NULL!COALESCE(party_zip, 0)
回答by cream
I got it by using AND (partyfn IS NOT NULL AND partyfn != '')
我通过使用得到它 AND (partyfn IS NOT NULL AND partyfn != '')
