[英]mysql select all records where a datetime field is less than a specified value
[英]MySQL Select all where DATETIME field is not NULL
我无法从此查询中选择适当的值:
SELECT * FROM discounts
WHERE DiscLimit > 0 AND DiscLimit >= DiscRedeemed
OR DiscExp IS NOT NULL AND DiscExp <= NOW()
DiscExp
是DATETIME
字段,默认为NULL
。
我正在尝试从数据库中选择当前未过期的折扣:
SELECT * FROM discounts WHERE
:
似乎正在检索DATETIME
字段为NULL
。 任何帮助将非常感激。
您需要括号! 尝试这个:
SELECT * FROM discounts
WHERE (DiscLimit > 0 AND DiscLimit >= DiscRedeemed)
OR (DiscExp IS NOT NULL AND DiscExp <= NOW())
但是,从您的问题来看,我不确定OR
是否正确。 如果您希望它满足以下所有条件:
你要这个:
SELECT * FROM discounts
WHERE DiscLimit > 0 AND DiscLimit >= DiscRedeemed
AND DiscExp IS NOT NULL AND DiscExp <= NOW()
或者,如果您希望它满足以下所有条件:
你要这个:
SELECT * FROM discounts
WHERE DiscLimit > 0 AND DiscLimit >= DiscRedeemed
AND (DiscExp IS NULL OR DiscExp <= NOW())
请注意,实际上您不需要使用DiscExp IS NOT NULL AND DiscExp <= NOW()
,因为NULL
不会评估为<= anything
DiscExp IS NOT NULL AND DiscExp <= NOW()
。
希望这可以帮助!
您的逻辑问题是括号。 但是,您可以编写:
SELECT d.*
FROM discounts d
WHERE DiscLimit > 0 AND
DiscLimit >= DiscRedeemed AND
DiscExp <= NOW();
NULL
比较是不必要的,因为当一个或两个操作数为NULL
时,任何比较运算符都将返回true。
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