MySQL 更新导致列值在查询中途更改

Question

谁能解释为什么在 MySQL 中会发生这种情况？

mysql> select * from test;
+----+---+---+
| id | a | b |
+----+---+---+
|  1 | 1 | 1 |
+----+---+---+
1 row in set

mysql> update test set a = a + 1, b = a + 1;
Query OK, 1 row affected
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select * from test;
+----+---+---+
| id | a | b |
+----+---+---+
|  1 | 2 | 3 |
+----+---+---+
1 row in set

mysql> 

架构:

CREATE TABLE `test` (
  `id` int(10) unsigned NOT NULL,
  `a` int(10) unsigned NOT NULL,
  `b` int(10) unsigned NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

Answer 1

据我了解，sql 执行从左到右的评估。因此，如果您更新 a 中的值并将 a 用作 b 的基础。新的值(value)将得到体现

SQL UPDATE order of evaluation