如何编写WHERE来等同于两列包含NULL和空值

Question

鉴于是我的表结构，现在我需要编写一个查询来比较“STRVAL1和STRVAL2”然后“BVAL1和BVAL2”，如果两者不相同，那么应该返回该行。

预期结果......

请使用以下数据的文字说明

DECLARE @TAB TABLE (ID INT, STRVAL1 VARCHAR(8), STRVAL2 VARCHAR(8), BVAL1 BIT, BVAL2 BIT)

    INSERT INTO @TAB VALUES 
      (1, NULL, NULL, NULL, NULL)
    , (2, '', NULL, NULL, NULL)
    , (3, '', '', NULL, NULL)
    , (4, 'VAL', 'VAL', NULL, NULL)
    , (5, 'VAL1', 'VAL2', NULL, NULL)
    , (6, NULL, NULL, 0, NULL)
    , (7, NULL, NULL, 0, 0)
    , (8, NULL, NULL, 1, 1)
    , (9, NULL, NULL, 1, 0)

    SELECT ID, STRVAL1, STRVAL2, BVAL1, BVAL2
    FROM @TAB

Answer 1

你可以使用比较，虽然NULL使这有点麻烦：

select t.*
from @tab t
where ((strval1 <> strval2) or
       (strval1 is null and strval2 is not null) or
       (strval1 is not null and strval2 is null)
      ) or
      ((bval1 <> bval2) or
       (bval1 is null and bval2 is not null) or
       (bval1 is not null and bval2 is null)
      );

Answer 2

您需要组合测试。

select ... from ... where
(strval1 is null and strval2 is not null) or
(strval1 is not null and strval2 is null) or
(strval1 != strval2) or
(bval1 is null and bval2 is not null) or
(bval1 is not null and bval2 is null) or
(bval1 != bval2)