MySQL exception handler access exception being handled

MySQL exception handler access exception being handled

I'm trying to rollback on an error, but still let the client receive the
error. This might actually be impossible, unless there is a way to access
the error in an exception handler.
It's possible to "throw" from an exception, i.e. it's possible to raise a
signal:
CREATE PROCEDURE p ()
BEGIN
DECLARE EXIT HANDLER FOR SQLEXCEPTION
BEGIN
SIGNAL SQLSTATE VALUE '99999'
SET MESSAGE_TEXT = 'An error occurred';
END;
DROP TABLE no_such_table;
END;
But this sample code from the MySQL doc looks horrible, because it
literally swallows all errors and jams them into one.
SHOW ERRORS seems relevant, but I don't see any way to work with it
programmatically, e.g. SELECT Code FROM (SHOW ERRORS); is not possible.
Is this possible? Is there a better practice that I'm missing entirely?