How can I get the set difference of two result sets?
Say I have a result set (just one column in each):
result1:
'a'
'b'
'c'
result2:
'b'
'c'
I want to minus what is in result1 by result2: result1 - result2 such that it equals:
difference of result1 - result2:
'a'
To perform result1 - result2, you can join result1 with result2, and only output items that exist in result1. For example:
SELECT DISTINCT result1.column
FROM result1 LEFT JOIN result2 ON result1.column = result2.column
WHERE result2.column IS NULL
Note that is not a set difference, and won't output items in result2 that don't exist in result1. It's set subtraction.
See also: Web archive'd version of relevant blog post.