SELECT 'X' AS line
SELECT 'X ' AS line
you will only get 1 value returned.
Well this is not a bug apparently it's a feature of the ANSI SQL-92 standard.
From section 8.2
If the length in characters of X is not equal to the length
in characters of Y, then the shorter string is effectively
replaced, for the purposes of comparison, with a copy of
itself that has been extended to the length of the longer
string by concatenation on the right of one or more pad char-
acters, where the pad character is chosen based on CS. If
CS has the NO PAD attribute, then the pad character is an
implementation-dependent character different from any char-
acter in the character set of X and Y that collates less
than any string under CS. Otherwise, the pad character is a
Blimey so SQL pads the shorter string with spaces!
Thanks to StackOverflow for that one.