Update with Case Statement fails because of nulls

Question

I have a column in a table of which I would like to swap the current value with another for particular entries. I am getting a no null constraint when clearly I am not leaving it empty.

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

Add a where clause:

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');

You could also solve this with ELSE direction. However, that is not as good because it attempts to update rows that do not need to be updated.