bug record - is not equal to a certain value, the query does not include attention is null (due to NULL values can not be compared directly with the arithmetic operator for that row in order to also check out NULL, then, only IS NULL.)

 

 

Not equal to a certain value, pay attention to the situation after the query does not include empty (NULL because the value can not be compared directly with the arithmetic operators. To put that line is also NULL check out, it can only use IS NULL)