mysql事件之修改事件（ALTER EVENT）、禁用事件（DISABLE）、啟用事件（ENABLE）、事件重新命名及資料庫事件遷移操作詳解
阿新 • • 發佈：2020-01-09
本文例項講述了mysql事件之修改事件（ALTER EVENT）、禁用事件（DISABLE）、啟用事件（ENABLE）、事件重新命名及資料庫事件遷移操作。分享給大家供大家參考，具體如下：
我們要知道，MySQL允許我們更改現有事件的各種屬性。如果我們要更改現有事件，可以使用ALTER EVENT語句，如下所示：
ALTER EVENT event_name ON SCHEDULE schedule ON COMPLETION [NOT] PRESERVE RENAME TO new_event_name ENABLE | DISABLE DO event_body
ALTER EVENT語句僅適用於存在的事件，如果我們嘗試修改不存在的事件，MySQL將會發出一條錯誤訊息，因此在更改事件之前，應先使用SHOW EVENTS語句檢查事件的存在：
mysql> SHOW EVENTS FROM testdb; +--------+---------------+----------------+-----------+----------+---------------------+----------------+----------------+--------+------+----------+------------+----------------------+----------------------+--------------------+ | Db | Name | Definer | Time zone | Type | Execute at | Interval value | Interval field | Starts | Ends | Status | Originator | character_set_client | collation_connection | Database Collation | +--------+---------------+----------------+-----------+----------+---------------------+----------------+----------------+--------+------+----------+------------+----------------------+----------------------+--------------------+ | testdb | test_event_02 | root@localhost | SYSTEM | ONE TIME | 2017-08-03 04:24:48 | NULL | NULL | NULL | NULL | DISABLED | 0 | utf8 | utf8_general_ci | utf8_general_ci | +--------+---------------+----------------+-----------+----------+---------------------+----------------+----------------+--------+------+----------+------------+----------------------+----------------------+--------------------+ 1 row in set
建立一個每分鐘將一條新記錄插入到messages表中的示例事件來演示如何使用ALTER EVENT語句的各種功能：
USE testdb;
CREATE EVENT test_event_04
ON SCHEDULE EVERY 1 MINUTE
DO
INSERT INTO messages(message,created_at)
VALUES('Test ALTER EVENT statement',NOW());
我們來把事件修改為為每2分鐘執行一次：
ALTER EVENT test_event_04 ON SCHEDULE EVERY 2 MINUTE;
我們還可以通過指定新的邏輯來更改事件的主體程式碼：
ALTER EVENT test_event_04
DO
INSERT INTO messages(message,created_at)
VALUES('Message from event',NOW());
-- 清空表中的資料
truncate messages;
修改完成後，可以等待2分鐘，再次檢視messages表：
mysql> SELECT * FROM messages; +----+--------------------+---------------------+ | id | message | created_at | +----+--------------------+---------------------+ | 1 | Message from event | 2017-08-03 04:46:47 | | 2 | Message from event | 2017-08-03 04:48:47 | +----+--------------------+---------------------+ 2 rows in set
我們可以在ALTER EVENT語句之後使用DISABLE關鍵字來禁用某個事件：
ALTER EVENT test_event_04 DISABLE;
我們也可以通過使用SHOW EVENTS語句來檢視事件的狀態：
mysql> SHOW EVENTS FROM testdb; +--------+---------------+----------------+-----------+-----------+---------------------+----------------+----------------+---------------------+------+----------+------------+----------------------+----------------------+--------------------+ | Db | Name | Definer | Time zone | Type | Execute at | Interval value | Interval field | Starts | Ends | Status | Originator | character_set_client | collation_connection | Database Collation | +--------+---------------+----------------+-----------+-----------+---------------------+----------------+----------------+---------------------+------+----------+------------+----------------------+----------------------+--------------------+ | testdb | test_event_02 | root@localhost | SYSTEM | ONE TIME | 2017-08-03 04:24:48 | NULL | NULL | NULL | NULL | DISABLED | 0 | utf8 | utf8_general_ci | utf8_general_ci | | testdb | test_event_04 | root@localhost | SYSTEM | RECURRING | NULL | 2 | MINUTE | 2017-08-03 04:44:47 | NULL | DISABLED | 0 | utf8 | utf8_general_ci | utf8_general_ci | +--------+---------------+----------------+-----------+-----------+---------------------+----------------+----------------+---------------------+------+----------+------------+----------------------+----------------------+--------------------+ 2 rows in set
我們可以在ALTER EVENT語句之後使用ENABLE關鍵字來啟用事件：
ALTER EVENT test_event_04 ENABLE;
檢視下事件狀態：
mysql> SHOW EVENTS FROM testdb; +--------+---------------+----------------+-----------+-----------+---------------------+----------------+----------------+---------------------+------+----------+------------+----------------------+----------------------+--------------------+ | Db | Name | Definer | Time zone | Type | Execute at | Interval value | Interval field | Starts | Ends | Status | Originator | character_set_client | collation_connection | Database Collation | +--------+---------------+----------------+-----------+-----------+---------------------+----------------+----------------+---------------------+------+----------+------------+----------------------+----------------------+--------------------+ | testdb | test_event_02 | root@localhost | SYSTEM | ONE TIME | 2017-08-03 04:24:48 | NULL | NULL | NULL | NULL | DISABLED | 0 | utf8 | utf8_general_ci | utf8_general_ci | | testdb | test_event_04 | root@localhost | SYSTEM | RECURRING | NULL | 2 | MINUTE | 2017-08-03 04:44:47 | NULL | ENABLED | 0 | utf8 | utf8_general_ci | utf8_general_ci | +--------+---------------+----------------+-----------+-----------+---------------------+----------------+----------------+---------------------+------+----------+------------+----------------------+----------------------+--------------------+ 2 rows in set
我們再來嘗試使用ALTER EVENT重新命名現有事件：
ALTER EVENT test_event_04 RENAME TO test_event_05;
來檢視下事件狀態：
mysql> SHOW EVENTS FROM testdb; +--------+---------------+----------------+-----------+-----------+---------------------+----------------+----------------+---------------------+------+----------+------------+----------------------+----------------------+--------------------+ | Db | Name | Definer | Time zone | Type | Execute at | Interval value | Interval field | Starts | Ends | Status | Originator | character_set_client | collation_connection | Database Collation | +--------+---------------+----------------+-----------+-----------+---------------------+----------------+----------------+---------------------+------+----------+------------+----------------------+----------------------+--------------------+ | testdb | test_event_02 | root@localhost | SYSTEM | ONE TIME | 2017-08-03 04:24:48 | NULL | NULL | NULL | NULL | DISABLED | 0 | utf8 | utf8_general_ci | utf8_general_ci | | testdb | test_event_05 | root@localhost | SYSTEM | RECURRING | NULL | 2 | MINUTE | 2017-08-03 04:44:47 | NULL | ENABLED | 0 | utf8 | utf8_general_ci | utf8_general_ci | +--------+---------------+----------------+-----------+-----------+---------------------+----------------+----------------+---------------------+------+----------+------------+----------------------+----------------------+--------------------+ 2 rows in set
完事再來通過使用RENAME TO子句將事件從一個數據庫移動到另一個數據庫中：
ALTER EVENT testdb.test_event_05 RENAME TO newdb.test_event_05;
再來檢視事件狀態：
mysql> SHOW EVENTS FROM newdb; +-------+---------------+----------------+-----------+-----------+------------+----------------+----------------+---------------------+------+---------+------------+----------------------+----------------------+--------------------+ | Db | Name | Definer | Time zone | Type | Execute at | Interval value | Interval field | Starts | Ends | Status | Originator | character_set_client | collation_connection | Database Collation | +-------+---------------+----------------+-----------+-----------+------------+----------------+----------------+---------------------+------+---------+------------+----------------------+----------------------+--------------------+ | newdb | test_event_05 | root@localhost | SYSTEM | RECURRING | NULL | 2 | MINUTE | 2017-08-03 04:44:47 | NULL | ENABLED | 0 | utf8 | utf8_general_ci | utf8_general_ci | +-------+---------------+----------------+-----------+-----------+------------+----------------+----------------+---------------------+------+---------+------------+----------------------+----------------------+--------------------+ 1 row in set
好啦，本次記錄就到這裡了。
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希望本文所述對大家MySQL資料庫計有所幫助。