1. 确实，本地可构建个类似的语句来复现，不知缘由：

*（ V 站排版原因，开头有全角空格。若要复制运行，记得删除）*

```mysql
WITH
　 nums(num) AS (
　　 VALUES ROW(1), ROW(2), ROW(3)
　)

SELECT @total, @total := sum(num)
FROM nums, (SELECT @total := 0) t
GROUP BY num;
```



2. 如果你只是想要『上一行的数据』，你可以使用*（连 SQLite 都支持的）*窗口函数 `LAG`：

```sql
WITH
　 nums(num) AS (
　　 VALUES ROW(1), ROW(2), ROW(3) -- SQLite 写法：VALUES (1), (2), (3)
　)

SELECT num, LAG(num) OVER(ORDER BY num)
FROM nums;
```



3. 另外，[MySQL 官方文档]( https://dev.mysql.com/doc/refman/8.0/en/user-variables.html ) 很不推荐你图片中的用法：

- 除了 `SET` 语句外，不应在同一条语句内赋值和读取一个用户变量*（ 5.7 版本文档：As a general rule, other than in SET statements, you should never assign a value to a user variable and read the value within the same statement ）*

- 涉及用户变量的表达式的求值顺序未定义*（ 8.0 版本文档：The order of evaluation for expressions involving user variables is undefined. For example, there is no guarantee that SELECT @a, @a:=@a+1 evaluates @a first and then performs the assignment ）*

- 『在 `SELECT` 中使用 `:=` 为用户变量赋值』已被弃用，未来会移除*（ 8.0 版本文档：Previous releases of MySQL made it possible to assign a value to a user variable in statements other than SET. This functionality is supported in MySQL 8.0 for backward compatibility but is subject to removal in a future release of MySQL ）*