一、MySQL触发器
触发器是由MySQL的基本命令事件来触发某种特定操作，这些基本的命令由INSERT、UPDATE、DELETE等事件来触发某些特定操作。满足触发器的触发条件时，数据库系统就会自动执行触发器中定义的程序语句。这样可以令某些操作之间的一致性得到协调。
1.创建MySQL触发器
mysql> CREATE TABLE IF NOT EXISTS tb_booklog(
-> id int(11) PRIMARY KEY auto_increment NOT NULL,
-> event varchar(200) NOT NULL,
-> logtime timestamp NOT NULL DEFAULT current_timestamp
-> );
Query OK, 0 rows affected (0.03 sec)
mysql> DELIMITER //
mysql> CREATE TRIGGER auto_save_log BEFORE INSERT
-> ON tb_bookinfo FOR EACH ROW
-> INSERT INTO tb_booklog(event,logtime) values('look at me',now());
-> //
Query OK, 0 rows affected (0.01 sec)
mysql> SELECT * FROM tb_bookinfo;
-> //
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
| 17120108 | Lian | 1 | QiaoJiang | 116 | 50.00 | 351 | 2 | 2018-04-18 | 0 | 2 |
| 17120109 | Tian King | 2 | TianJiang | 117 | 51.10 | 352 | 3 | 2018-04-19 | 0 | 3 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
3 rows in set (0.00 sec)
mysql> INSERT INTO tb_bookinfo
-> (barcode,bookname,typeid,author,ISBN,price,page,bookcase,inTime,del,id)
-> VALUES
-> ('17120110','ShenOba',4,'ShenJiang','118',52.15,300,4,'2018-04-20',0,4);
-> //
Query OK, 1 row affected (0.00 sec)
mysql> SELECT * FROM tb_bookinfo;
-> //
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
| 17120108 | Lian | 1 | QiaoJiang | 116 | 50.00 | 351 | 2 | 2018-04-18 | 0 | 2 |
| 17120109 | Tian King | 2 | TianJiang | 117 | 51.10 | 352 | 3 | 2018-04-19 | 0 | 3 |
| 17120110 | ShenOba | 4 | ShenJiang | 118 | 52.15 | 300 | 4 | 2018-04-20 | 0 | 4 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
4 rows in set (0.00 sec)
mysql> SELECT * FROM tb_booklog;
-> //
+----+------------+---------------------+
| id | event | logtime |
+----+------------+---------------------+
| 2 | look at me | 2018-04-18 19:40:02 |
+----+------------+---------------------+
1 row in set (0.00 sec)
2.创建具有多个执行语句的触发器
mysql> CREATE DEFINER=`root`@`localhost` TRIGGER delete_book_info BEFORE DELETE
-> ON tb_bookinfo FOR EACH ROW
-> BEGIN
-> INSERT INTO tb_booklog(event,logtime) values('let me go',now());
-> INSERT INTO tb_bookinfobak SELECT * FROM tb_bookinfo where id=OLD.id;
-> END
-> //
Query OK, 0 rows affected (0.01 sec)
血一般惨痛的教训！！！当删除表中某一条记录未能成功时，检查一下触发器什么的有没有INSERT INTO语句，如果有，检查插入值的个数和表能不能对应起来，这里的原因就是两个表不一致！！！
Microsoft Windows [版本 10.0.16299.371]
(c) 2017 Microsoft Corporation。保留所有权利。
C:UsersBigJun>mysql -uroot -p
Enter password: *********
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 23
Server version: 5.7.20 MySQL Community Server (GPL)
Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or 'h' for help. Type 'c' to clear the current input statement.
mysql> DELIMITER //
mysql> CREATE DEFINER=`root`@`localhost` TRIGGER BEFORE DELETE
-> ON tb_bookinfo FOR EACH ROW
-> BEGIN
-> INSERT INTO tb_booklog(event,logtime) values('let me go'.now());
-> INSERT INTO tb_bookinfobak SELECT * FROM tb_bookinfo where id=OLD.id;
-> END
-> //
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'BEFORE DELETE
ON tb_bookinfo FOR EACH ROW
BEGIN
INSERT INTO tb_booklog(event,log' at line 1
mysql> CREATE DEFINER=`root`@`localhost` TRIGGER delete_book_info BEFORE DELETE
-> ON tb_bookinfo FOR EACH ROW
-> BEGIN
-> INSERT INTO tb_booklog(event,logtime) values('let me go'.now());
-> INSERT INTO tb_bookinfobak SELECT * FROM tb_bookinfo where id=OLD.id;
-> END
-> //
ERROR 1046 (3D000): No database selected
mysql> use db_library;
ERROR 1049 (42000): Unknown database 'db_library;'
mysql> USE db_library;
ERROR 1049 (42000): Unknown database 'db_library;'
mysql> exit
Bye
C:UsersBigJun>mysql -uroot -p
Enter password: *********
Welcome to the MySQL monitor. Commands end with ; or g.
Your MySQL connection id is 24
Server version: 5.7.20 MySQL Community Server (GPL)
Copyright (c) 2000, 2017, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or 'h' for help. Type 'c' to clear the current input statement.
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| db_database13 |
| db_library |
| db_library1 |
| db_library_gbk |
| hotel |
| mybatis |
| mysql |
| mysqldb |
| performance_schema |
| se |
| spring |
| springapp |
| sys |
| test |
+--------------------+
15 rows in set (0.00 sec)
mysql> use db_library;
Database changed
mysql> DELIMITER //
mysql> CREATE DEFINER=`root`@`localhost` TRIGGER delete_book_info BEFORE DELETE
-> ON tb_bookinfo FOR EACH ROW
-> BEGIN
-> INSERT INTO tb_booklog(event,logtime) values('let me go'.now());
->
-> INSERT INTO tb_bookinfobak SELECT * FROM tb_bookinfo where id=OLD.id;
-> END
-> //
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '.now());
INSERT INTO tb_bookinfobak SELECT * FROM tb_bookinfo where id=OLD.id;
' at line 4
mysql> CREATE DEFINER=`root`@`localhost` TRIGGER delete_book_info BEFORE DELETE
-> ON tb_bookinfo FOR EACH ROW
-> BEGIN
-> INSERT INTO tb_booklog(event,logtime) values('let me go'.now());
-> INSERT INTO tb_bookinfobak SELECT * FROM tb_bookinfo where id=OLD.id;
-> END
-> //
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '.now());
INSERT INTO tb_bookinfobak SELECT * FROM tb_bookinfo where id=OLD.id;
E' at line 4
mysql> CREATE DEFINER=`root`@`localhost` TRIGGER delete_book_info BEFORE DELETE
-> ON tb_bookinfo FOR EACH ROW
-> BEGIN
-> INSERT INTO tb_booklog(event,logtime) values('let me go',now());
-> INSERT INTO tb_bookinfobak SELECT * FROM tb_bookinfo where id=OLD.id;
-> END
-> //
Query OK, 0 rows affected (0.01 sec)
mysql> select * from tb_bookinfo;
-> //
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
| 17120108 | Lian | 1 | QiaoJiang | 116 | 50.00 | 351 | 2 | 2018-04-18 | 0 | 2 |
| 17120109 | Tian King | 2 | TianJiang | 117 | 51.10 | 352 | 3 | 2018-04-19 | 0 | 3 |
| 17120110 | ShenOba | 4 | ShenJiang | 118 | 52.15 | 300 | 4 | 2018-04-20 | 0 | 4 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
4 rows in set (0.01 sec)
mysql> select * from tb_booklog;
-> //
+----+------------+---------------------+
| id | event | logtime |
+----+------------+---------------------+
| 2 | look at me | 2018-04-18 19:40:02 |
+----+------------+---------------------+
1 row in set (0.00 sec)
mysql> select * from tb_bookinfobak;
-> //
Empty set (0.00 sec)
mysql> DELETE FROM tb_bookinfo where id=4;
-> //
ERROR 1136 (21S01): Column count doesn't match value count at row 1
mysql> DELETE FROM tb_bookinfo WHERE id=4;
-> //
ERROR 1136 (21S01): Column count doesn't match value count at row 1
mysql> DELETE FROM tb_bookinfo WHERE id=3;
-> //
ERROR 1136 (21S01): Column count doesn't match value count at row 1
mysql> DELETE FROM tb_bookinfo WHERE barcode='17120107';
-> //
ERROR 1136 (21S01): Column count doesn't match value count at row 1
mysql> show triggers;
-> //
+------------------+--------+-------------+--------------------------------------------------------------------------------------------------------------------------------------------------+--------+------------------------+-------------------------------------------------------------------------------------------------------------------------------------------+----------------+----------------------+----------------------+--------------------+
| Trigger | Event | Table | Statement | Timing | Created | sql_mode | Definer | character_set_client | collation_connection | Database Collation |
+------------------+--------+-------------+--------------------------------------------------------------------------------------------------------------------------------------------------+--------+------------------------+-------------------------------------------------------------------------------------------------------------------------------------------+----------------+----------------------+----------------------+--------------------+
| delete_book_info | DELETE | tb_bookinfo | BEGIN
INSERT INTO tb_booklog(event,logtime) values('let me go',now());
INSERT INTO tb_bookinfobak SELECT * FROM tb_bookinfo where id=OLD.id;
END | BEFORE | 2018-04-18 20:35:07.19 | 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 | root@localhost | gbk | gbk_chinese_ci | utf8_general_ci |
+------------------+--------+-------------+--------------------------------------------------------------------------------------------------------------------------------------------------+--------+------------------------+-------------------------------------------------------------------------------------------------------------------------------------------+----------------+----------------------+----------------------+--------------------+
1 row in set (0.00 sec)
mysql> select * from tb_bookinfo;
-> //
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
| 17120108 | Lian | 1 | QiaoJiang | 116 | 50.00 | 351 | 2 | 2018-04-18 | 0 | 2 |
| 17120109 | Tian King | 2 | TianJiang | 117 | 51.10 | 352 | 3 | 2018-04-19 | 0 | 3 |
| 17120110 | ShenOba | 4 | ShenJiang | 118 | 52.15 | 300 | 4 | 2018-04-20 | 0 | 4 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
4 rows in set (0.00 sec)
mysql> delete from tb_bookinfo where id=1;
-> //
ERROR 1136 (21S01): Column count doesn't match value count at row 1
mysql> desc tb_bookinfobak;
-> //
+------------+------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+------------+------------------+------+-----+---------+-------+
| barcode | varchar(30) | YES | | NULL | |
| bookname | varchar(70) | YES | | NULL | |
| typeid | int(10) unsigned | YES | | NULL | |
| author | varchar(30) | YES | | NULL | |
| ISBN | varchar(20) | YES | | NULL | |
| price | float(8,2) | YES | | NULL | |
| page | int(10) unsigned | YES | | NULL | |
| bookcase | int(10) unsigned | YES | | NULL | |
| inTime | datetime(6) | YES | | NULL | |
| del | tinyint(1) | YES | | 0 | |
| id | int(11) | NO | | NULL | |
| translator | varchar(30) | NO | | NULL | |
+------------+------------------+------+-----+---------+-------+
12 rows in set (0.00 sec)
mysql> alter table tb_bookinfobak drop transtor;
-> //
ERROR 1091 (42000): Can't DROP 'transtor'; check that column/key exists
mysql> alter table tb_bookinfobak drop translator;
-> //
Query OK, 0 rows affected (0.04 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc tb_bookinfobak;
-> //
+----------+------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------+------+-----+---------+-------+
| barcode | varchar(30) | YES | | NULL | |
| bookname | varchar(70) | YES | | NULL | |
| typeid | int(10) unsigned | YES | | NULL | |
| author | varchar(30) | YES | | NULL | |
| ISBN | varchar(20) | YES | | NULL | |
| price | float(8,2) | YES | | NULL | |
| page | int(10) unsigned | YES | | NULL | |
| bookcase | int(10) unsigned | YES | | NULL | |
| inTime | datetime(6) | YES | | NULL | |
| del | tinyint(1) | YES | | 0 | |
| id | int(11) | NO | | NULL | |
+----------+------------------+------+-----+---------+-------+
11 rows in set (0.00 sec)
mysql> desc tb_bookinfo;
-> //
+----------+------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------+------+-----+---------+-------+
| barcode | varchar(30) | YES | | NULL | |
| bookname | varchar(70) | YES | | NULL | |
| typeid | int(10) unsigned | YES | | NULL | |
| author | varchar(30) | YES | | NULL | |
| ISBN | varchar(20) | YES | | NULL | |
| price | float(8,2) | YES | | NULL | |
| page | int(10) unsigned | YES | | NULL | |
| bookcase | int(10) unsigned | YES | | NULL | |
| inTime | date | YES | | NULL | |
| del | tinyint(1) | YES | | 0 | |
| id | int(11) | NO | PRI | NULL | |
+----------+------------------+------+-----+---------+-------+
11 rows in set (0.00 sec)
mysql> alter table tb_bookinfobak modify inTime date;
-> //
Query OK, 0 rows affected (0.04 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> desc tb_bookinfobak;
-> //
+----------+------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------+------+-----+---------+-------+
| barcode | varchar(30) | YES | | NULL | |
| bookname | varchar(70) | YES | | NULL | |
| typeid | int(10) unsigned | YES | | NULL | |
| author | varchar(30) | YES | | NULL | |
| ISBN | varchar(20) | YES | | NULL | |
| price | float(8,2) | YES | | NULL | |
| page | int(10) unsigned | YES | | NULL | |
| bookcase | int(10) unsigned | YES | | NULL | |
| inTime | date | YES | | NULL | |
| del | tinyint(1) | YES | | 0 | |
| id | int(11) | NO | | NULL | |
+----------+------------------+------+-----+---------+-------+
11 rows in set (0.00 sec)
mysql> select * from tb_bookinfo;
-> //
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
| 17120108 | Lian | 1 | QiaoJiang | 116 | 50.00 | 351 | 2 | 2018-04-18 | 0 | 2 |
| 17120109 | Tian King | 2 | TianJiang | 117 | 51.10 | 352 | 3 | 2018-04-19 | 0 | 3 |
| 17120110 | ShenOba | 4 | ShenJiang | 118 | 52.15 | 300 | 4 | 2018-04-20 | 0 | 4 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
4 rows in set (0.00 sec)
mysql> select * from tb_bookbak;
-> //
ERROR 1146 (42S02): Table 'db_library.tb_bookbak' doesn't exist
mysql> select * from tb_bookinfobak;
-> //
Empty set (0.00 sec)
mysql> select * from tb_booklog;
-> //
+----+------------+---------------------+
| id | event | logtime |
+----+------------+---------------------+
| 2 | look at me | 2018-04-18 19:40:02 |
+----+------------+---------------------+
1 row in set (0.00 sec)
mysql> delete from tb_bookinfo where id=1;
-> //
Query OK, 1 row affected (0.01 sec)
mysql> select * from tb_bookinfobak;
-> //
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| barcode | bookname | typeid | author | ISBN | price | page | bookcase | inTime | del | id |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
| 17120107 | Java King | 3 | LianJiang | 115 | 49.80 | 350 | 1 | 2018-04-17 | 0 | 1 |
+----------+-----------+--------+-----------+------+-------+------+----------+------------+------+----+
1 row in set (0.00 sec)
mysql> select * from tb_booklog;
-> //
+----+------------+---------------------+
| id | event | logtime |
+----+------------+---------------------+
| 2 | look at me | 2018-04-18 19:40:02 |
| 8 | let me go | 2018-04-18 20:54:19 |
+----+------------+---------------------+
2 rows in set (0.00 sec)
二、查看触发器
1.SHOW TRIGGER语句
mysql> SHOW TRIGGERsG
*************************** 1. row ***************************
Trigger: delete_book_info
Event: DELETE
Table: tb_bookinfo
Statement: BEGIN
INSERT INTO tb_booklog(event,logtime) values('let me go',now());
INSERT INTO tb_bookinfobak SELECT * FROM tb_bookinfo where id=OLD.id;
END
Timing: BEFORE
Created: 2018-04-18 20:35:07.19
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: gbk
collation_connection: gbk_chinese_ci
Database Collation: utf8_general_ci
1 row in set (0.00 sec)
2.查看triggers表中的触发信息
（1）查看所有触发器的定义
mysql> SELECT * FROM information_schema.triggersG
*************************** 1. row ***************************
TRIGGER_CATALOG: def
TRIGGER_SCHEMA: db_library
TRIGGER_NAME: delete_book_info
EVENT_MANIPULATION: DELETE
EVENT_OBJECT_CATALOG: def
EVENT_OBJECT_SCHEMA: db_library
EVENT_OBJECT_TABLE: tb_bookinfo
ACTION_ORDER: 1
ACTION_CONDITION: NULL
ACTION_STATEMENT: BEGIN
INSERT INTO tb_booklog(event,logtime) values('let me go',now());
INSERT INTO tb_bookinfobak SELECT * FROM tb_bookinfo where id=OLD.id;
END
ACTION_ORIENTATION: ROW
ACTION_TIMING: BEFORE
ACTION_REFERENCE_OLD_TABLE: NULL
ACTION_REFERENCE_NEW_TABLE: NULL
ACTION_REFERENCE_OLD_ROW: OLD
ACTION_REFERENCE_NEW_ROW: NEW
CREATED: 2018-04-18 20:35:07.19
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: gbk
COLLATION_CONNECTION: gbk_chinese_ci
DATABASE_COLLATION: utf8_general_ci
*************************** 2. row ***************************
TRIGGER_CATALOG: def
TRIGGER_SCHEMA: sys
TRIGGER_NAME: sys_config_insert_set_user
EVENT_MANIPULATION: INSERT
EVENT_OBJECT_CATALOG: def
EVENT_OBJECT_SCHEMA: sys
EVENT_OBJECT_TABLE: sys_config
ACTION_ORDER: 1
ACTION_CONDITION: NULL
ACTION_STATEMENT: BEGIN IF @sys.ignore_sys_config_triggers != true AND NEW.set_by IS NULL THEN SET NEW.set_by = USER(); END IF; END
ACTION_ORIENTATION: ROW
ACTION_TIMING: BEFORE
ACTION_REFERENCE_OLD_TABLE: NULL
ACTION_REFERENCE_NEW_TABLE: NULL
ACTION_REFERENCE_OLD_ROW: OLD
ACTION_REFERENCE_NEW_ROW: NEW
CREATED: 2018-01-08 16:14:42.70
SQL_MODE:
DEFINER: mysql.sys@localhost
CHARACTER_SET_CLIENT: utf8
COLLATION_CONNECTION: utf8_general_ci
DATABASE_COLLATION: utf8_general_ci
*************************** 3. row ***************************
TRIGGER_CATALOG: def
TRIGGER_SCHEMA: sys
TRIGGER_NAME: sys_config_update_set_user
EVENT_MANIPULATION: UPDATE
EVENT_OBJECT_CATALOG: def
EVENT_OBJECT_SCHEMA: sys
EVENT_OBJECT_TABLE: sys_config
ACTION_ORDER: 1
ACTION_CONDITION: NULL
ACTION_STATEMENT: BEGIN IF @sys.ignore_sys_config_triggers != true AND NEW.set_by IS NULL THEN SET NEW.set_by = USER(); END IF; END
ACTION_ORIENTATION: ROW
ACTION_TIMING: BEFORE
ACTION_REFERENCE_OLD_TABLE: NULL
ACTION_REFERENCE_NEW_TABLE: NULL
ACTION_REFERENCE_OLD_ROW: OLD
ACTION_REFERENCE_NEW_ROW: NEW
CREATED: 2018-01-08 16:14:42.70
SQL_MODE:
DEFINER: mysql.sys@localhost
CHARACTER_SET_CLIENT: utf8
COLLATION_CONNECTION: utf8_general_ci
DATABASE_COLLATION: utf8_general_ci
3 rows in set (0.03 sec)
（2）查看指定触发器名称的触发器的定义（指定数据库时将NAME改成SCHEMA，等号后面改成数据库名）
mysql> SELECT * FROM information_schema.triggers WHERE TRIGGER_NAME='delete_book_info'G;
*************************** 1. row ***************************
TRIGGER_CATALOG: def
TRIGGER_SCHEMA: db_library
TRIGGER_NAME: delete_book_info
EVENT_MANIPULATION: DELETE
EVENT_OBJECT_CATALOG: def
EVENT_OBJECT_SCHEMA: db_library
EVENT_OBJECT_TABLE: tb_bookinfo
ACTION_ORDER: 1
ACTION_CONDITION: NULL
ACTION_STATEMENT: BEGIN
INSERT INTO tb_booklog(event,logtime) values('let me go',now());
INSERT INTO tb_bookinfobak SELECT * FROM tb_bookinfo where id=OLD.id;
END
ACTION_ORIENTATION: ROW
ACTION_TIMING: BEFORE
ACTION_REFERENCE_OLD_TABLE: NULL
ACTION_REFERENCE_NEW_TABLE: NULL
ACTION_REFERENCE_OLD_ROW: OLD
ACTION_REFERENCE_NEW_ROW: NEW
CREATED: 2018-04-18 20:35:07.19
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: gbk
COLLATION_CONNECTION: gbk_chinese_ci
DATABASE_COLLATION: utf8_general_ci
1 row in set (0.01 sec)
三、使用触发器
1.触发器的执行顺序
mysql> create table if not exists tb_temp(
-> id int(11) PRIMARY KEY auto_increment NOT NULL,
-> event varchar(200) NOT NULL,
-> time timestamp NOT NULL DEFAULT current_timestamp
-> );
Query OK, 0 rows affected (0.03 sec)
mysql> create table tb_bookcase(
-> id int(11) PRIMARY KEY auto_increment NOT NULL,
-> name varchar(200)
-> );
Query OK, 0 rows affected (0.02 sec)
mysql> create trigger before_in BEFORE INSERT ON
-> tb_bookcase FOR EACH ROW
-> INSERT INTO tb_temp(event) values('BEFORE INSERT');
Query OK, 0 rows affected (0.01 sec)
mysql> create trigger after_in AFTER INSERT ON
-> tb_bookcase FOR EACH ROW
-> INSERT INTO tb_temp(event) values('AFTER INSERT');
Query OK, 0 rows affected (0.01 sec)
mysql> select * from tb_bookcase;
Empty set (0.00 sec)
mysql> select * from tb_temp;
Empty set (0.00 sec)
mysql> INSERT INTO tb_bookcase(name) VALUES('左边第二个');
Query OK, 1 row affected (0.01 sec)
mysql> select * from tb_bookcase;
+----+-----------------+
| id | name |
+----+-----------------+
| 1 | 左边第二个 |
+----+-----------------+
1 row in set (0.00 sec)
mysql> select * from tb_temp;
+----+---------------+---------------------+
| id | event | time |
+----+---------------+---------------------+
| 1 | BEFORE INSERT | 2018-04-19 08:17:28 |
| 2 | AFTER INSERT | 2018-04-19 08:17:28 |
+----+---------------+---------------------+
2 rows in set (0.00 sec)
2.使用触发器维护冗余数据（为了避免数据不一致问题的发生，尽量不要人工维护数据，建议通过编程自动维护）
mysql> create table tb_stock(
-> id int(11) PRIMARY KEY auto_increment NOT NULL.
-> id int(11) PRIMARY KEY auto_increment NOT NULL.^C
mysql> create table tb_stock(
-> id int(11) PRIMARY KEY auto_increment NOT NULL,
-> goodsname varchar(200) NOT NULL,
-> number int(11)
-> );
Query OK, 0 rows affected (0.02 sec)
mysql> select * from tb_stock; +----+-------------+--------+ | id | goodsname | number | +----+-------------+--------+ | 1 | 小猪佩qi | 100 | +----+-------------+--------+ 1 row in set (0.00 sec)
mysql> create table tb_sell(
-> id int(11) PRIMARY KEY auto_increment NOT NULL,
-> goodsname varchar(200),
-> number int(11)
-> );
-> //
Query OK, 0 rows affected (0.02 sec)
mysql> select * from tb_sell;
-> //
Empty set (0.00 sec)
mysql> CREATE TRIGGER auto_number AFTER INSERT
-> ON tb_sell FOR EACH ROW
-> BEGIN
-> DECLARE sellnum int(10);
-> SELECT number FROM tb_sell where id=NEW.id INTO @sellnum;
-> UPDATE tb_stock SET number=number-@sellnum WHERE goodsname='小猪佩qi';
-> END
-> //
Query OK, 0 rows affected (0.01 sec)
mysql> INSERT INTO tb_sell(goodsname,number) VALUES
-> ('小猪佩qi',2);
-> //
Query OK, 1 row affected (0.01 sec)
mysql> select * from tb_sell;
-> //
+----+-------------+--------+
| id | goodsname | number |
+----+-------------+--------+
| 1 | 小猪佩qi | 2 |
+----+-------------+--------+
1 row in set (0.00 sec)
mysql> select * from tb_stock;
-> //
+----+-------------+--------+
| id | goodsname | number |
+----+-------------+--------+
| 1 | 小猪佩qi | 98 |
+----+-------------+--------+
1 row in set (0.00 sec)
四、删除触发器