Sorry, but you're wrong :-)
I'm using the HEX representation only between the Perl script and the SQL-Server. You could still do a

SELECT LastLogin FROM Users WHERE Username="astroboy"
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Note the " around your name, they make this a string.
Try this with your SQL-Server:

SELECT 1 WHERE "astroboy"=0x617374726f626f79
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PS: You could also use SQL commands to play with your string, because the SQL server trade it as a plain string, not a list of HEX-codes:

SELECT 1 FROM Users WHERE LOWER(Username)=LOWER(0x617374726f626f79) AN
+D Password=0x617374726f626f79
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This would match astroboy, ASTROBOY and AstroBoy in the DB, but not 0x617374726f626f79 or 0x617374726F626F79.