MYSQL 语法不评估不等于存在 NULL
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MYSQL syntax not evaluating not equal to in presence of NULL
提问by user1904273
I am having trouble with a mysql query. I want to exclude values of 2. So I thought I would do following:
我在使用 mysql 查询时遇到问题。我想排除 2 的值。所以我想我会做以下事情：
table products
id | name | backorder
-------------------
1 | product1 | NULL
2 | product2 | NULL
3 | product3 | 2
SELECT name from `products` p
WHERE backorder <> '2'
However, This is not giving the desired result of product1, product 2 It is giving an empty results table.
但是，这并没有给出 product1 的预期结果，product 2 它给出了一个空的结果表。
On the other hand if I use
另一方面，如果我使用
SELECT name from `products` p
WHERE backorder = '2'
Then it produces: product3. But I want to get those records where it is not equal to 2.
然后它产生：product3。但我想得到那些不等于的记录2。
Something is not working with the <> '2'. Could it be that the NULLvalues are throwing it off? Can anyone suggest a fix.
某些东西不适用于<> '2'. 难道是NULL价值观把它扔掉了？任何人都可以建议修复。
Thanks in advance!
提前致谢！
回答by John Woo
use IS NULLor IS NOT NULLto compare NULLvalues because they are simply unknown.
使用IS NULL或IS NOT NULL来比较NULL值，因为它们只是未知的。
SELECT name
from products p
WHERE backorder IS NULL OR backorder <> 2
回答by simhumileco
You can use:
您可以使用：
SELECT `name` FROM `products` `p`
WHERE NOT `backorder` <=> '2'
or
或者
SELECT `name` FROM `products` `p`
WHERE !(`backorder` <=> '2')
回答by jbkhere
Sorry to open this
抱歉打开这个
We can use this also
我们也可以使用这个
SELECT name
from products p
WHERE COALESCE(backorder,1) <> 2
回答by sentil kumar
Try this and see.
试试这个，看看。
SELECT name from `products` p
WHERE backorder != '2'
