MySQL实现类似Oracle中的nextval和currval

CREATE TABLE `sequence` (
  `seq_name` varchar(50) NOT NULL,
  `current_val` int(11) NOT NULL,
  `increment_val` int(11) NOT NULL DEFAULT '1',
  PRIMARY KEY (`seq_name`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
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CREATE DEFINER=`root`@`localhost` FUNCTION `currval`(v_seq_name VARCHAR(50)) RETURNS int(11)
begin 
    declare value integer; 
    set value = 0; 
    select current_val into value 
    from sequence 
    where seq_name = v_seq_name; 
    return value; 
end
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CREATE DEFINER=`root`@`localhost` FUNCTION `nextval`(v_seq_name VARCHAR(50)) RETURNS int(11)
begin 
  update sequence 
  set current_val = current_val + increment_val 
  where seq_name = v_seq_name;
  return currval(v_seq_name); 
end