MySQL实现自增序列

参考：https://blog.csdn.net/weixin_42383575/article/details/103023379

新建序列

### 新建序列表
drop table if exists sequence;
create table sequence(
seq_name VARCHAR(50)  NOT NULL COMMENT '序列名称',
current_val INT             NOT NULL COMMENT '当前值',    
increment_val INT         NOT NULL     DEFAULT 1 COMMENT '跨度',
PRIMARY KEY(seq_name)
);

### 新增一个序列
INSERT INTO sequence VALUES('seq_test_1', 0, 1);
INSERT INTO sequence VALUES('seq_test_2', 0, 2);

### 创建函数用于获取当前序列值
CREATE FUNCTION currval(v_seq_name VARCHAR(50))
    RETURNS INTEGER
BEGIN
    DECLARE val INTEGER;
    set val = 0;
    SELECT current_val into val from sequence where seq_name=v_seq_name;
    return val;
END;

### 查询当前的值
SELECT currval('seq_test_1');

### 创建函数用户获取下一个值
CREATE FUNCTION nextval(v_seq_name VARCHAR(50))
    RETURNS INTEGER
BEGIN
    UPDATE sequence SET current_val = current_val + increment_val where seq_name=v_seq_name;
    return currval(v_seq_name);
END;

### 查询下一个值
SELECT nextval('seq_test_1');

创建表测试

### 新建测试表
DROP TABLE IF EXISTS `sequence_test`;
CREATE TABLE `sequence_test` (
  `name` varchar(255) NOT NULL,
  `value` double(255,2) DEFAULT NULL,
  `num1` int(11) DEFAULT NULL,
  `num2` int(11) DEFAULT NULL,
  PRIMARY KEY (`name`)
);

### 新建触发器 插入记录前给自增字段赋值
DROP TRIGGER IF EXISTS `TRI_TEST_SEQ`;
CREATE TRIGGER `TRI_TEST_SEQ` BEFORE INSERT ON `sequence_test` FOR EACH ROW BEGIN
SET NEW.num1 = nextval('seq_test_1');
SET NEW.num2 = nextval('seq_test_2');
END;


### 测试效果
INSERT INTO sequence_test(name, value) VALUES('1', 111);
INSERT INTO sequence_test(name, value) VALUES('2', 111);
INSERT INTO sequence_test(name, value) VALUES('3', 111);
INSERT INTO sequence_test(name, value) VALUES('4', 111);

### 结果展示
SELECT * FROM sequence_test;