MYSQL返回行

Question

我有一个带有mysql记录的表，如下所示，我想得到结果，如果在receivefmuser和topm中没有值那么将显示没有记录（表示0行），但是mysql不能用作mysql仍然算作1排？

select receivedfmuser, topm from tb_postatus where pono = 36 and receivedfmuser is not null and topm is not null


TABLE
|tid|pono|receivedfmuser|topm      |
|1  |36  |02/02/2015    |          |
|2  |27  |02/03/2015    |02/03/2015|

Answer 1

在上面的示例中，row1中topm中的值实际上是一个空字符串值，而不是NULL。这就是它满足not null条件并显示记录的原因。所以，使用以下

select receivedfmuser, topm from tb_postatus 
where pono = 36 and 
receivedfmuser != '' and 
topm != ''

这不显示具有NULL的行以及具有空字符串值的行。

Answer 2

尝试以下查询

select receivedfmuser, topm 
    from tb_postatus 
    where pono = 36 
    and receivedfmuser is not null
    and receivedfmuser != ""
    and topm is not null
    and topm != ""

Answer 3

如果在上面的示例中，您检查null的值是topm，则问题是您的查询，因为您的查询正在验证＆＃34; receivedfmuser＆＃34;因为不是空值。

select t.receivedfmuser, t.topm, t.pono
from test t
where `receivedfmuser` IS NOT NULL;

receivedfmuser，topm，pono

＆＃39; 02/02 / 2015＆＃39;，NULL，＆＃39; 36＆＃39; ＆＃39; 02/02 / 2015＆＃39;，＆＃39; 02/03 / 2015＆＃39;，＆＃39; 27＆＃39;

然后将查询更改为＆＃34; topm＆＃34;

select t.receivedfmuser, t.topm, t.pono
from test t
where `topm` IS NOT NULL;

receivedfmuser，topm，pono

＆＃39; 02/02 / 2015＆＃39;，＆＃39; 02/03 / 2015＆＃39;，＆＃39; 27＆＃39;

结果显示1行，topm非空。

用你的例子：

select t.receivedfmuser, t.topm, t.pono
from test t
where `topm` IS NOT NULL and t.pono = 36;

receivedfmuser，topm，pono

不返回结果。

希望这有帮助。

是的，如果您检查的值为null实际上是一个空值，则查询将无效，因为mysql不会将null理解为空字符串。