mysql生成id

CREATE DEFINER=`root`@`%` FUNCTION `SnowId`() RETURNS bigint(20)
BEGIN
	
	DECLARE b_current_time BIGINT;
	DECLARE b_time_tick BIGINT;
	DECLARE i_work_id INT;
	DECLARE i_work_id_big_length INT;
	DECLARE i_seq_big_length INT;
	DECLARE f_random FLOAT;
	
	DECLARE b_res BIGINT;
	
	SET i_work_id = 1;
	SET i_work_id_big_length = 4;
	SET i_seq_big_length = 8;
	SET b_current_time = (REPLACE(UNIX_TIMESTAMP(CURRENT_TIMESTAMP(3)),'.','')) + 0;
	SET b_time_tick = b_current_time - 1582136402000;
	SET f_random = RAND();
	
	SET b_res = b_time_tick * POWER(2, i_work_id_big_length + i_seq_big_length) + i_work_id * POWER(2, i_seq_big_length) + (5 + round((POWER(2, i_seq_big_length)-1) * f_random, 0));
	
	RETURN b_res;
END