rocknbil - 7:37 pm on Apr 7, 2010 (gmt 0)
To add to the mix . . . if you set up your database correctly, you will have an expected value for uninitialized field.s That is, if NULL does it for you, you need only test for null.
UPDATE table SET
column1 = 'value1'
WHERE column2 = 'value1' AND column1 IS NULL;
If there's a possibility you'd insert a blank string in there, then it will no longer be NULL, so go with the or . . .