MySQL触发器是否会激活其他触发器？

Question

例如，如果我定义了一个触发器，当该帖子被删除时删除该帖子的所有评论。当用户被删除时删除所有帖子的触发器会激活另一个触发器从而删除评论吗？

Answer 1

简短的回答是肯定的。

演示：

mysql> create table users (id serial primary key);

mysql> create table posts (id serial primary key, userid bigint unsigned);

mysql> create table comments (id serial primary key, postid bigint unsigned);

mysql> create trigger udel after delete on users for each row delete from posts where userid = OLD.id;

mysql> create trigger pdel after delete on posts for each row delete from comments where postid = OLD.id;

mysql> insert into users values (123);
Query OK, 1 row affected (0.00 sec)

mysql> insert into posts values (456, 123);
Query OK, 1 row affected (0.00 sec)

mysql> insert into comments values (789, 456);
Query OK, 1 row affected (0.00 sec)

mysql> select * from users;
+-----+
| id  |
+-----+
| 123 |
+-----+
1 row in set (0.00 sec)

mysql> select * from posts;
+-----+--------+
| id  | userid |
+-----+--------+
| 456 |    123 |
+-----+--------+
1 row in set (0.00 sec)

mysql> select * from comments;
+-----+--------+
| id  | postid |
+-----+--------+
| 789 |    456 |
+-----+--------+

现在我们尝试删除，它应该级联到其他表：

mysql> delete from users;
Query OK, 1 row affected (0.03 sec)

mysql> select * from posts;
Empty set (0.00 sec)

mysql> select * from comments;
Empty set (0.00 sec)