SQL 没有 WHERE 子句的 SELECT NOT NULL 值
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SELECT NOT NULL values without WHERE clause
提问by Hélder Gon?alves
Is there a way to select not null values without a where clause? i know it can be done like this
有没有办法在没有 where 子句的情况下选择非空值？我知道可以这样做
SELECT X, Y, Z
FROM T
WHERE X IS NOT NULL
but Im wondering if there is a way to put the null 'filter' in the select clause without using the where
但我想知道是否有一种方法可以在不使用 where 的情况下将空“过滤器”放在 select 子句中
maybe something like this?
也许是这样的？
SELECT NOT_NULL(X), Y, Z
FROM T
Ty
泰
回答by SQLMenace
no, there is no way, if you need to filter stuff out you need a WHERE clause. That said, you can change the values returned from null to something else by using ISNULL or COALESCE
不，没有办法，如果你需要过滤掉东西，你需要一个 WHERE 子句。也就是说，您可以使用 ISNULL 或 COALESCE 将返回的值从 null 更改为其他值
回答by Lasse Edsvik
Are you looking for COALESCE?
您在寻找 COALESCE 吗？
i.e
IE
SELECT COALESCE(HasBananas, 'No') FROM Sometable
回答by digscoop
I can't see one sane reason to do this, but you could filter through a JOIN clause if you really don't want a WHERE.
我看不出这样做的合理理由，但如果您真的不想要 WHERE，您可以过滤 JOIN 子句。
SELECT X, Y, Z
FROM T
JOIN (SELECT null a) Q ON X IS NOT NULL
回答by valex
Why not :) But WHERE is MUCH better.
为什么不:) 但哪里更好。
The trick here is in JOIN ONcondition where if you compare anything with NULLit is always FALSEeven NULL=NULLis FALSE.
这里的技巧是在 JOINON条件下，如果你与NULL它比较任何东西总是FALSE偶数NULL=NULL是FALSE.
select * from t
join
(
select distinct x from t
) t1 on (t.x=t1.x);
回答by Ramon de Klein
If you just want to check if a value is NULL and return it as a boolean in your result, then you can use something like this:
如果您只想检查一个值是否为 NULL 并将其作为布尔值返回到您的结果中，那么您可以使用以下方法：
SELECT CASE
WHEN X IS NULL THEN 0
ELSE 1
END AS XisNull,
Y,
Z
FROM T
If you just want to filter, then use the WHERE statement. It has been created for it :-)
如果您只想过滤，请使用 WHERE 语句。它是为它创建的:-)
