由于空值，用Case语句更新失败

Question

我在表中有一列，我想将当前值与另一个用于特定条目的值交换。显然我没有把它留空时，我得到了一个没有空约束。

UPDATE bet.betEntry
SET direction= 
            CASE 
                WHEN (direction = '599065F7-96A9-4DF5-8577-2203BE9AA2E0') THEN  'ABD92DB9-58D8-4C60-8A34-4C00EBBAB4A5'
                WHEN (direction = 'ABD92DB9-58D8-4C60-8A34-4C00EBBAB4A5') THEN '599065F7-96A9-4DF5-8577-2203BE9AA2E0'
         END    
FROM bet.betEntry be JOIN bet.fixture f ON  be.fixtureId = f.fixtureId
WHERE f.fixtureDate > '2019-01-12 13:29:00.000'

Answer 1

添加一个where子句：

UPDATE bet.betEntry
    SET direction = (CASE WHEN direction = '599065F7-96A9-4DF5-8577-2203BE9AA2E0'
                          THEN  'ABD92DB9-58D8-4C60-8A34-4C00EBBAB4A5'
                          WHEN direction = 'ABD92DB9-58D8-4C60-8A34-4C00EBBAB4A5'
                          THEN '599065F7-96A9-4DF5-8577-2203BE9AA2E0'
                     END)   
FROM bet.betEntry be JOIN
     bet.fixture f
     ON  be.fixtureId = f.fixtureId
WHERE f.fixtureDate > '2019-01-12 13:29:00.000' AND
      direction IN ('599065F7-96A9-4DF5-8577-2203BE9AA2E0', '599065F7-96A9-4DF5-8577-2203BE9AA2E0');

您也可以使用ELSE direction解决此问题。但是，这样做并不好，因为它尝试更新不需要更新的行。

Answer 2

您的ELSE引起了问题，您可以添加where子句（direction IN ('599065F7-96A9-4DF5-8577-2203BE9AA2E0', '599065F7-96A9-4DF5-8577-2203BE9AA2E0')）或添加else（ELSE direction）：

UPDATE bet.betEntry
     SET direction = (CASE WHEN direction = '599065F7-96A9-4DF5-8577-2203BE9AA2E0'
                           THEN 'ABD92DB9-58D8-4C60-8A34-4C00EBBAB4A5'
                           WHEN direction = 'ABD92DB9-58D8-4C60-8A34-4C00EBBAB4A5'
                           THEN '599065F7-96A9-4DF5-8577-2203BE9AA2E0'
                           ELSE direction             
                      END)    
FROM bet.betEntry be JOIN
     bet.fixture f
     ON  be.fixtureId = f.fixtureId
WHERE f.fixtureDate > '2019-01-12 13:29:00.000';