There are two basic rules used compare character values in Oracle.
Blank-padded Comparison
Blank-padded comparison is used with CHAR, NCHAR, text
literals or values returned by the USER function. Here if two values have different lengths,
then blanks are added to the shorter one such that their lengths are
equal. Then values are compared
character by character up to the first character that differs. The value with
the greater character at the first differing position is considered as greater.
Non-padded Comparison
This is used with VARCHAR2 or NVARCHAR2. Here no padding is
used. Instead oracle compares two values character by character up to the first
character that differs. The value with
the greater character in that position is considered greater. If the lengths of
the two comparing values are different and the values are identical up to the
end of the shorter longer value is considered greater.
Here I have mentioned a small example on how blank-padded comparison and non-padded comparison will behave when comparing two string values.
Comparing 'a ' and 'a'
'a ' = 'a' is TRUE with blank-padded comparison
but with non-padded comparison it is TRUE
