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如果我們銷毀與其關聯的表，觸發器也會被銷毀。這稱為觸發器的顯式銷毀。可以通過一個例子來理解 –

示例

假設我們在名為“Sample”的表上有一個名為“trigger_before_delete_sample”的觸發器。現在，如果我們刪除該表，那么與該表關聯的上述觸發器也將被刪除。

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)

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上面的結果集顯示數據庫中有兩個觸發器，其中一個觸發器與名為“Sample”的表關聯。現在，借助以下語句，我們將刪除該表 –

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

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現在借助以下語句，我們可以看到與名為“Sample”的表關聯的觸發器也被銷毀了。

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)

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