"reverse()" on strings

Hi,
CREATE TABLE file (name varchar(255));
I have a couple of milion filenames. I need to build index based on 
extensions. A couple of possibilities come to mind:
CREATE INDEX extension_idx ON file (reverse(name));
-- but I didn't find a function called "reverse"
CREATE INDEX extension_idx ON file (regex_match( '.*(\.[^\.]*)$' );
-- but I didn't find a function called "regex_match" which would return
string matched in brackets ()

Any ideas ? Help ? Hints ?

  Thanks in advance !
     John


PS: if there is reverse on strings -- where could I find "reverse()" on 
arrays ? - thx

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