MySQL 5.5 Release Notes
If a stored procedure exits with an unhandled exception,
modified values of OUT and
INOUT parameters are not propogated back to
the caller.
If an exception is handled by a CONTINUE or
EXIT handler that contains a
RESIGNAL statement, execution of
RESIGNAL signals the exception
(that is, the information that existed before entry into the
handler). If the exception is an error, the values of
OUT and INOUT parameters
are not propogated back to the caller.