Question

我有3个MySQL表（food，apple和orange）。

我想删除以下行：

apple(idapple, iduser, name) 
orange(idornge, iduser, name)

使用一个触发器删除food(iduser, name)中的行？

到目前为止，这是我的触发器：

  CREATE TRIGGER `food_before_delete`

    AFTER DELETE ON `food` 
    FOR EACH ROW 

      DELETE FROM apple, orange 
      WHERE 
      apple.iduser=OLD.iduser and 
      orange.iduser=OLD.iduser

但它不会编译。如何制作一次从两个表中删除的触发器？

Answer 1

使用触发器一次从两个表中删除：

触发器用于强制表中的数据完整性。您可以使用触发器一次删除任意数量的表。

在初始化触发器之前，我们需要临时更改mysql定界符运算符，因为触发器使用分号;运算符在触发器中指定多个sql命令。

步骤1更改当前分隔符：

delimiter $$

步骤2创建触发器：

CREATE TRIGGER `blog_before_delete`     
  AFTER DELETE ON `blog`     
  FOR EACH ROW     
BEGIN
  DELETE FROM blog_tags where blogid = OLD.id;
  DELETE FROM blog_comments where blogid = OLD.id;
END
$$

步骤3恢复上一个分隔符：

delimiter ;

<强>解释

OLD是内置关键字，指的是我们要删除的博客表行。每当我们删除博客表中的条目时，Mysql就会运行触发器blog_before_delete。我的触发器失败，然后回滚删除。这有助于确保我们数据库中的Atomicity, Consistency, Isolation, and Durability。

Answer 2

CREATE TRIGGER `food_before_delete`     
AFTER DELETE ON `food`     
FOR EACH ROW     
begin
  DELETE FROM apple
  WHERE apple.iduser=NEW.iduser;

  DELETE FROM orange
  WHERE orange.iduser=NEW.iduser;
end

delete语句可能需要OLD.iduser，不支持NEW.iduser。查看您的手册。

Answer 3

可能更简单吗？

DELETE f,a,o FROM
food AS f 
LEFT JOIN apple AS a USING (iduser)
LEFT JOIN orange AS o USING (iduser)
WHERE f.name = ...

无需触发器。

Answer 4

我忘记了触发器中的BEGIN和END块。你必须按顺序从表中删除：

CREATE TRIGGER `food_before_delete`     
  AFTER DELETE ON `food`     
  FOR EACH ROW     
BEGIN
  DELETE FROM apple
  WHERE apple.iduser=NEW.iduser;

  DELETE FROM orange
  WHERE orange.iduser=NEW.iduser; 
END

Answer 5

使用一个触发器触发删除两个表的MySQL演练：

<强> 1。登录

el@apollo:~$ mysql -u root -p
Enter password: 
mysql> use your_database;
Database changed

<强> 2。创建一些测试表并插入行：

mysql> create table derp(derp1 INT);
Query OK, 0 rows affected (0.02 sec)

mysql> create table foo(foo1 INT);
Query OK, 0 rows affected (0.02 sec)

mysql> create table bar(bar1 INT);
Query OK, 0 rows affected (0.02 sec)

mysql> insert into derp values (1);
Query OK, 1 row affected (0.01 sec)

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

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

第3。触发：

mysql> delimiter //
mysql> create trigger delete_foo_and_bar_when_derp_is_deleted
    -> after delete on derp
    -> for each row
    -> begin
    -> delete from foo where foo1=OLD.derp1;
    -> delete from bar where bar1=OLD.derp1;
    -> end//
Query OK, 0 rows affected (0.02 sec)

<强> 4。请参阅表格，并填写所有三个。

mysql> delimiter ;
mysql> select * from derp;
+-------+
| derp1 |
+-------+
|     1 |
+-------+
1 row in set (0.00 sec)

mysql> select * from foo;
+------+
| foo1 |
+------+
|    1 |
+------+
1 row in set (0.00 sec)

mysql> select * from bar;
+------+
| bar1 |
+------+
|    1 |
+------+
1 row in set (0.00 sec)

<强> 5。从derp中删除

mysql> delete from derp where derp1 = 1;
Query OK, 1 row affected (0.01 sec)

<强> 6。看到derp，foo和bar现在都是空的：

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

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

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

我想在MySQL中从2个表中删除一个触发器

5 个答案:

使用一个触发器触发删除两个表的MySQL演练：