mysql nextval同步锁_如何实现mysql线程安全的nextval()方法

-- 表

CREATE TABLE `sequence_data` (

`sequence_name` varchar(100) NOT NULL,

`sequence_increment` int(11) unsigned NOT NULL DEFAULT 1,

`sequence_min_value` int(11) unsigned NOT NULL DEFAULT 1,

`sequence_max_value` bigint(20) unsigned NOT NULL DEFAULT 18446744073709551615,

`sequence_cur_value` bigint(20) unsigned DEFAULT 1,

`sequence_cycle` boolean NOT NULL DEFAULT FALSE,

PRIMARY KEY (`sequence_name`)

);

-- 函数

delimiter //

CREATE FUNCTION `nextval` (`seq_name` varchar(100))

RETURNS bigint(20) NOT DETERMINISTIC

BEGIN

DECLARE cur_val bigint(20);

SELECT

sequence_cur_value INTO cur_val

FROM

sequence_data

WHERE

sequence_name = seq_name

;

IF cur_val IS NOT NULL THEN

UPDATE

sequence_data

SET

sequence_cur_value = IF (

(sequence_cur_value + sequence_increment) > sequence_max_value,

IF (

sequence_cycle = TRUE,

sequence_min_value,

NULL

),

sequence_cur_value + sequence_increment

)

WHERE

sequence_name = seq_name

;

END IF;

RETURN cur_val;

END

//

delimiter ;

-- insert new sequence

-- INSERT INTO sequence_data (sequence_name) VALUE ('sq_my_sequence');

-- 调用

-- SELECT nextval('sq_my_sequence') as nextval