mysql - 插入表中选择 max(column_name)+1

Question

我有这样构建的 mysql 表:

CREATE TABLE `posts` (
    `post_id` INT(10) NOT NULL AUTO_INCREMENT,
    `post_user_id` INT(10) NOT NULL DEFAULT '0',
    `gen_id` INT(10) NOT NULL DEFAULT '0',
    PRIMARY KEY (`post_user_id`, `post_id`)
)
COLLATE='utf8_general_ci'
ENGINE=MyISAM;

当我这样做时:

insert into posts (post_user_id) values (1);
insert into posts (post_user_id) values (1);
insert into posts (post_user_id) values (2);
insert into posts (post_user_id) values (1);
select * from posts;

我得到:

post_id | post_user_id | gen_id
1                  1     0
2                  1     0
1                  2     0
3                  1     0

为每个唯一用户生成一个唯一的 post_id。

我需要 gen_id 列为 1 2 3 4 5 6 等。我如何在插入时增加此列。我试过下面的那个，但它不起作用。执行此操作的正确方法是什么？

insert into posts (post_user_id,gen_id) values (1,select max(gen_id)+1 from posts);
//Select the highest gen_id and add 1 to it.

Answer 1

试试这个:

  INSERT INTO posts (post_user_id,gen_id) 
  SELECT 1, MAX(gen_id)+1 FROM posts;