'Returns database block with the highest sequence number lower than the block\'s sequence_number
:param block: The block who\'s predecessor we want to find
:return A block'

def get_block_before(self, block):

    return self._get(u'WHERE    sequence_number    <    ?    AND    public_key    =    ?    ORDER    BY    sequence_number    DESC', (block.sequence_number, buffer(block.public_key)))
