当我们删除具有该触发器的表时，触发器会发生什么情况？-mysql教程-PHP中文网

当我们删除具有该触发器的表时，触发器会发生什么情况？

如果我们销毁与其关联的表，触发器也会被销毁。这称为触发器的显式销毁。可以通过一个例子来理解 -

示例

假设我们在名为“Sample”的表上有一个名为“trigger_before_delete_sample”的触发器。现在，如果我们删除该表，那么与该表关联的上述触发器也将被删除。

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mysql> Show Triggers\G
*************************** 1. row ***************************
              Trigger: trigger_before_delete_sample
                Event: DELETE
                Table: sample
            Statement: BEGIN
         SET @count = if (@count IS NULL, 1, (@count+1));
         INSERT INTO sample_rowaffected values (@count);
END
               Timing: BEFORE
              Created: 2017-11-21 12:31:58.70
             sql_mode: ONLY_FULL_GROUP_BY,
                       STRICT_TRANS_TABLES,
                       NO_ZERO_IN_DATE,
                       NO_ZERO_DATE,
                       ERROR_FOR_DIVISION_BY_ZERO,
                       NO_AUTO_CREATE_USER,
                       NO_ENGINE_SUBSTITUTION
              Definer: root@localhost
 character_set_client: cp850
 collation_connection: cp850_general_ci
   Database Collation: latin1_swedish_ci
*************************** 2. row ***************************
              Trigger: before_inser_studentage
                Event: INSERT
                Table: student_age
            Statement: IF NEW.age < 0 THEN SET NEW.age = 0;
END IF
               Timing: BEFORE
              Created: 2017-11-21 11:26:15.34
             sql_mode: ONLY_FULL_GROUP_BY,
                       STRICT_TRANS_TABLES,
                       NO_ZERO_IN_DATE,
                       NO_ZERO_DATE,
                       ERROR_FOR_DIVISION_BY_ZERO,
                       NO_AUTO_CREATE_USER,
                       NO_ENGINE_SUBSTITUTION
              Definer: root@localhost
 character_set_client: cp850
 collation_connection: cp850_general_ci
   Database Collation: latin1_swedish_ci
2 rows in set (0.01 sec)

上面的结果集显示数据库中有两个触发器，其中一个触发器与名为“Sample”的表关联。现在，借助以下语句，我们将删除该表 -

mysql> DROP table sample;
Query OK, 0 rows affected (0.26 sec)

现在借助以下语句，我们可以看到与名为“Sample”的表关联的触发器也被销毁了。

mysql> Show Triggers\G
*************************** 1. row ***************************
              Trigger: before_inser_studentage
                Event: INSERT
                Table: student_age
            Statement: IF NEW.age < 0 THEN SET NEW.age = 0;
END IF
               Timing: BEFORE
              Created: 2017-11-21 11:26:15.34
             sql_mode: ONLY_FULL_GROUP_BY,
                       STRICT_TRANS_TABLES,
                       NO_ZERO_IN_DATE,
                       NO_ZERO_DATE,
                       ERROR_FOR_DIVISION_BY_ZERO,
                       NO_AUTO_CREATE_USER,
                       NO_ENGINE_SUBSTITUTION
              Definer: root@localhost
 character_set_client: cp850
 collation_connection: cp850_general_ci
   Database Collation: latin1_swedish_ci
1 row in set (0.01 sec)