我想要一个触发器从 MySQL 中的 2 个表中删除

Question

我有 3 个 MySQL 表（food、apple 和 orange）。

我想从以下位置删除行：

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

使用一个触发器删除 food(iduser, name) 中的一行时？

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。如何制作一个同时从两个表中删除的触发器？

Answer 1

使用触发器同时删除两个表：

触发器用于强制表中数据的完整性。您可以使用触发器一次从任意数量的表中删除。

在初始化触发器之前，我们需要暂时更改mysql分隔符运算符，因为触发器使用分号;运算符来指定触发器内的多个sql命令。

第 1 步更改当前分隔符：

delimiter $

第 2 步创建触发器：

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
$

第 3 步恢复先前的分隔符：

delimiter ;

说明：

OLD 是一个内置关键字，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。如果触发器失败，则回滚删除。这有助于确保我们的数据库的原子性、一致性、隔离性和持久性。

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

删除语句可能需要 OLD.iduser，但不支持 NEW.iduser。检查你的手册。

Answer 3

也许更简单的东西？

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。并且您必须按顺序从表中删除，如下所示：

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

MySQL 演练如何制作一个触发器，用一个触发器删除两个表：

1.登录：

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

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)

3.触发触发器：

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)

4.查看表是否存在并且所有三个表均已填充。

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)

5.从derp中删除

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

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)