SQL选择where子句操作<>

Question

i want to get column value that has some other value and null but don't want value that equal to some point.

Example

ID|VID  |IC  |
1 |v001 |123 |
2 |v001 |null|
3 |v003 |456 |
4 |v004 |null|

so i want to get ID which IC is not equal to 123. but i only get ID 3 but ID 2 and 4 will not shown out in sql. i have tried select * from table where IC<>'123' and IC is null but it shows nothing.

Answer 1

SELECT * FROM table WHERE IC != '123' OR IC IS NULL

Answer 2

You want OR , not AND :

select * from table where IC != 123 OR IC IS NULL

Any comparison with NULL produces the third logic value , UNKNOWN , and any negation of UNKNOWN produces UNKNOWN , so you have to treat the NULL s separately - but, of course, for any particular row, it cannot possibly be true that it's simultaneously got a value different from 123 but at the same time it's NULL . So AND is wrong.

Answer 3

Try the following:

SELECT *  
FROM table   
WHERE IC != '123'   
OR IC IS NULL  

Answer 4

尝试这个 ：

select * from table where ISNULL(IC,0)<>'123'