Порядок приоритета UPDATE для обновления нескольких таблиц

Question

Если у меня есть оператор UPDATE, где я делаю SET p.old_email = u.email, u.email = NULL, будет ли p.old_email = u.email всегда происходить до u.email = NULL? Причина, по которой я спрашиваю, я не наблюдаю такого поведения.

mysql> SHOW TRIGGERS; 
UPDATE 
Empty set (0.01 sec) 

mysql> 
mysql> UPDATE 
    -> users u INNER JOIN people p ON p.id = u.id INNER JOIN entities e ON e.id = p.id 
    -> SET p.old_username = NULL, p.username = 'myusername', 
    -> p.old_email = NULL, u.email = 'myemail@example.com', 
    -> e.record_status = 'inactive', e.date_modified = NOW(), e.modified_by_id =506836355 
    -> WHERE u.id =1753671666 AND u.id !=506836355 AND e.sites_id =2846702735; 
Query OK, 3 rows affected (0.00 sec) 
Rows matched: 3 Changed: 3 Warnings: 0 

mysql> 
mysql> SELECT p.old_username, p.username, p.old_email, u.email 
    -> FROM users u INNER JOIN people p ON p.id = u.id INNER JOIN entities e ON e.id = p.id 
    -> WHERE u.id =1753671666 AND u.id !=506836355 AND e.sites_id =2846702735; 
+--------------+------------+-----------+---------------------+ 
| old_username | username | old_email | email    | 
+--------------+------------+-----------+---------------------+ 
| NULL   | myusername | NULL  | myemail@example.com | 
+--------------+------------+-----------+---------------------+ 
1 row in set (0.00 sec) 

mysql> 
mysql> UPDATE 
    -> users u INNER JOIN people p ON p.id = u.id INNER JOIN entities e ON e.id = p.id 
    -> SET p.old_username = p.username, p.username = NULL 
    -> WHERE u.id =1753671666 AND u.id !=506836355 AND e.sites_id =2846702735; 
WHERE u.id =1753671666 AND u.id !=506836355 AND e.sites_id =2846702735Query OK, 1 row affected (0.00 sec); 

Rows matched: 1 Changed: 1 Warnings: 0 

mysql> 
mysql> SELECT p.old_username, p.username, p.old_email, u.email 
    -> FROM users u INNER JOIN people p ON p.id = u.id INNER JOIN entities e ON e.id = p.id 
    -> WHERE u.id =1753671666 AND u.id !=506836355 AND e.sites_id =2846702735; 
+--------------+----------+-----------+---------------------+ 
| old_username | username | old_email | email    | 
+--------------+----------+-----------+---------------------+ 
| myusername | NULL  | NULL  | myemail@example.com | 
+--------------+----------+-----------+---------------------+ 
1 row in set (0.00 sec) 

mysql> 
mysql> UPDATE 
    -> users u INNER JOIN people p ON p.id = u.id INNER JOIN entities e ON e.id = p.id 
    -> SET p.old_email = u.email, u.email = NULL 
    -> WHERE u.id =1753671666 AND u.id !=506836355 AND e.sites_id =2846702735; 
Query OK, 1 row affected (0.00 sec) 
Rows matched: 2 Changed: 1 Warnings: 0 

mysql> 
mysql> SELECT p.old_username, p.username, p.old_email, u.email 
    -> FROM users u INNER JOIN people p ON p.id = u.id INNER JOIN entities e ON e.id = p.id 
    -> WHERE u.id =1753671666 AND u.id !=506836355 AND e.sites_id =2846702735; 
+--------------+----------+-----------+-------+ 
| old_username | username | old_email | email | 
+--------------+----------+-----------+-------+ 
| myusername | NULL  | NULL  | NULL | 
+--------------+----------+-----------+-------+ 
1 row in set (0.00 sec) 

mysql> 
mysql> UPDATE 
    -> users u INNER JOIN people p ON p.id = u.id INNER JOIN entities e ON e.id = p.id 
    -> SET p.old_username = NULL, p.username = 'myusername', 
    -> p.old_email = NULL, u.email = 'myemail@example.com', 
    -> e.record_status = 'inactive', e.date_modified = NOW(), e.modified_by_id =506836355 
    -> WHERE u.id =1753671666 AND u.id !=506836355 AND e.sites_id =2846702735; 
Query OK, 2 rows affected (0.00 sec) 
Rows matched: 3 Changed: 2 Warnings: 0 

mysql> 
mysql> SELECT p.old_username, p.username, p.old_email, u.email 
    -> FROM users u INNER JOIN people p ON p.id = u.id INNER JOIN entities e ON e.id = p.id 
    -> WHERE u.id =1753671666 AND u.id !=506836355 AND e.sites_id =2846702735; 
+--------------+------------+-----------+---------------------+ 
| old_username | username | old_email | email    | 
+--------------+------------+-----------+---------------------+ 
| NULL   | myusername | NULL  | myemail@example.com | 
+--------------+------------+-----------+---------------------+ 
1 row in set (0.00 sec) 

mysql> 
mysql> UPDATE 
    -> users u INNER JOIN people p ON p.id = u.id INNER JOIN entities e ON e.id = p.id 
    -> SET p.old_username = p.username, p.username = NULL, 
    -> p.old_email = u.email, u.email = NULL, 
    -> e.record_status = 'inactive', e.date_modified = NOW(), e.modified_by_id =506836355 
    -> WHERE u.id =1753671666 AND u.id !=506836355 AND e.sites_id =2846702735; 
Query OK, 2 rows affected (0.00 sec) 
Rows matched: 3 Changed: 2 Warnings: 0 

mysql> 
mysql> SELECT p.old_username, p.username, p.old_email, u.email 
    -> FROM users u INNER JOIN people p ON p.id = u.id INNER JOIN entities e ON e.id = p.id 
    -> WHERE u.id =1753671666 AND u.id !=506836355 AND e.sites_id =2846702735; 
+--------------+----------+-----------+-------+ 
| old_username | username | old_email | email | 
+--------------+----------+-----------+-------+ 
| myusername | NULL  | NULL  | NULL | 
+--------------+----------+-----------+-------+ 
1 row in set (0.00 sec) 

mysql> 
mysql> 

Answer 1

От MySQL documentation:

Второе назначение в следующих наборах отчетности col2 к текущему (обновлено) col1 значению, а не оригинальному col1 значения. В результате col1 и col2 имеют одинаковое значение. Это поведение отличается от стандартного SQL.

UPDATE t1 SET col1 = col1 + 1, col2 = col1; 

однотабличное UPDATE назначение, как правило, вычисляется слева направо. Для обновлений с несколькими таблицами нет гарантии, что назначения выполняются в любом конкретном порядке.

Выполняется обновление нескольких таблиц, а назначение столбцов происходит не в определенном порядке, как указано в документации.