mysql创建序列

create table sequence(
name varchar(50) not null primary key,
current_value BIGINT not null DEFAULT 0,
increment int not null DEFAULT 1,
max_value BIGINT,  -- 最大值
initial_value BIGINT, -- 初始值，当当前值大于最大值，回到初始值
key (name)
);

DELIMITER ;; 
CREATE FUNCTION nextval (seq_name VARCHAR(50))  
RETURNS BIGINT  
CONTAINS SQL  
BEGIN  
UPDATE sequence  
SET current_value = current_value + increment  
WHERE name = seq_name;  
RETURN currval(seq_name);  
END;;  


drop function currval;
DELIMITER ;; 
CREATE FUNCTION currval (seq_name VARCHAR(50))  
RETURNS INTEGER  
CONTAINS SQL  
BEGIN  
SELECT current_value,max_value,initial_value INTO @current_value, @max_value, @initial_value
FROM sequence  
WHERE name = seq_name;
if(@current_value>@max_value) then 
UPDATE sequence  
SET current_value = initial_value  
WHERE name = seq_name;
set @current_value=@initial_value;
end if;
RETURN @current_value;  
END;;


SELECT * from sequence;

SELECT nextval('sq_test_id');