oracle - PL/SQL "between x and y" does not work, if y < x. Why?

Question

I have a PL/SQL code like:

case when column between 201203 and 201201
then other_column
end

I know that there are values in column that are 201203. So code should return some values. But it didn't until I corrected it like:

case when column between 201201 and 201203
then other_column
end

Why between keyword works like that? How it is implemented on Oracle Databases?

Answer 1

This is ANSI SQL behavior.

 expr1 BETWEEN expr2 AND expr3

translates to

 expr2 <= expr1 AND expr1 <= expr3