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借助 ALTER EVENT 語句，我們可以修改現有的 MySQL 事件。我們可以更改事件的各種屬性。ALTER EVENT 的語法如下：

   ALTER EVENT event_name
    ON SCHEDULE schedule
ON COMPLETION [NOT] PRESERVE
  RENAME TO new_event_name
    ENABLE | DISABLE
           DO
       event_body

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為了理解它，我們將舉例說明如下 –

示例

假設我們有一個事件，如下 –

mysql> Create event hello ON SCHEDULE EVERY 1 Minute DO INSERT INTO event_messages(message, generated_at) Values ('Alter event testing', NOW());
Query OK, 0 rows affected (0.00 sec)

mysql> select * from event_messages;
+----+---------------------+---------------------+
| ID | MESSAGE             | Generated_at        |
+----+---------------------+---------------------+
|  1 | Without Preserve    | 2017-11-22 20:32:13 |
|  2 | With Preserve       | 2017-11-22 20:35:12 |
|  3 | Alter event testing | 2017-11-22 21:08:37 |
+----+---------------------+---------------------+
3 rows in set (0.00 sec)

mysql> ALTER EVENT hello ON SCHEDULE EVERY 2 MINUTE;
Query OK, 0 rows affected (0.00 sec)

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上述查詢會將事件的時間表從 1 分鐘更改為 2 分鐘。下面的查詢將更改事件的正文。

mysql> ALTER EVENT hello DO INSERT INTO event_messages(message,generated_at) VALUES('ALTERED',NOW());
Query OK, 0 rows affected (0.00 sec)

mysql> select * from event_messages;
+----+---------------------+---------------------+
| ID | MESSAGE             | Generated_at        |
+----+---------------------+---------------------+
|  1 | Without Preserve    | 2017-11-22 20:32:13 |
|  2 | With Preserve       | 2017-11-22 20:35:12 |
|  3 | Alter event testing | 2017-11-22 21:08:37 |
|  4 | Alter event testing | 2017-11-22 21:09:15 |
|  5 | ALTERED             | 2017-11-22 21:11:15 |
+----+---------------------+---------------------+
5 rows in set (0.00 sec)

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上面的結果集顯示我們在2分鐘后收到了更改的消息。

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