mysql触发器学习
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触发器(trigger)是一个特殊的存储过程，他的执行不是由程序调用，也不是手工启动，而是由事件触发，比如当对一个表进行操作（insert,delete,update） 时就会激活它执行。触发器经常用于加强数据的完整性约束和业务规则等。 例如，当学生表中增加了一个学生的信息时，学生的总数就应该同时改变。 因此可以针对学生表创建一个触发器，每次增加一个学生记录时，就执行一次学生总数的计算操作，从而保证学生总数与记录数保持一致。 创建Trigger; 语法： CREATE TRIGGER 触发器名称 BEFORE|AFTER 触发事件 ON 表名 FOR EACH ROW BEGIN 触发器程序体; END <触发器名称> 最多64个字符，它和mysql中其他对象的命名方式一样。 {BEFORE|AFTER} 触发器时机 {INSERT|UPDATE|DELETE} 触发器事件 ON<表名称> 标识触发器的表名，即在那张表上建立触发器。 FOR EACH ROW 触发器的执行间隔:FOR EACH ROW 子句通知触发器每隔一行执行一次动作，而不是对整个表执行一次。 <触发器程序体> 触发器所要触发的SQL语句:语句可以使用顺序，判断，循环等语句，实现一般程序所需要的逻辑功能。 同一张表最多可以创建6个触发器(分别是insert BEFORE|AFTER...) 创建学生表： mysql> create table student( -> id int auto_increment primary key not null, -> name varchar(50) -> ); Query OK, 0 rows affected (0.02 sec) 插入一条数据： mysql> insert into student values(1,‘jack‘); Query OK, 1 row affected (0.00 sec) 创建student_total表： mysql> create table student_total(total int); Query OK, 0 rows affected (0.01 sec) example1: .创建存储器student_insert_trigger mysql> delimiter && mysql> create trigger student_insert_trigger after insert > on student for each row > BEGIN > update student_total set total=total+1; > END && mysql> delimiter ; mysql> insert into student values(2,‘tom‘); Query OK, 1 row affected (0.01 sec) mysql> select * from student_total; +-------+ | total | +-------+ | 2 | +-------+ 1 row in set (0.01 sec) 创建删除的trigger： mysql> create trigger student_delete_after after delete on student for each row BEGIN update student_total set total=total-1; END$$ Query OK, 0 rows affected (0.00 sec) mysql> delimiter ; 测试一下： 插入数据前： mysql> select * from student; +----+--------+ | id | name | +----+--------+ | 1 | jack | | 2 | tom | | 3 | jerry | | 10 | jastin | +----+--------+ 4 rows in set (0.00 sec) mysql> select * from student_total; +-------+ | total | +-------+ | 4 | +-------+ 1 row in set (0.00 sec) 删除一条记录： mysql> delete from student where name=‘jastin‘; Query OK, 1 row affected (0.00 sec) mysql> select * from student; +----+-------+ | id | name | +----+-------+ | 1 | jack | | 2 | tom | | 3 | jerry | +----+-------+ 3 rows in set (0.00 sec) mysql> select * from student_total; +-------+ | total | +-------+ | 3 | +-------+ 1 row in set (0.00 sec) 可以看到total数变为3; 查看触发器： mysql> show triggers\G *************************** 1. row *************************** Trigger: student_insert_trigger Event: INSERT Table: student Statement: BEGIN update student_total set total=total+1; END Timing: AFTER Created: 2017-04-03 00:59:37.56 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: utf8 collation_connection: utf8_general_ci Database Collation: utf8_general_ci *************************** 2. row *************************** Trigger: student_delete_after Event: DELETE Table: student Statement: BEGIN update student_total set total=total-1; END Timing: AFTER Created: 2017-04-03 01:19:05.27 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: utf8 collation_connection: utf8_general_ci Database Collation: utf8_general_ci 2 rows in set (0.01 sec) 也可以在information_schema库中查看： mysql> select * from information_schema.triggers\G 删除触发器： mysql> drop trigger student_delete_after; Query OK, 0 rows affected (0.02 sec) 触发器实例： example2 作用：增加tab1表记录后自动将记录增加到tab2表中 创建表tab1 DROP TABLE IF EXISTS tab1; CREATE TABLE tab1( tab1_id varchar(50) ); 创建表tab2 DROP TABLE IF EXISTS tab2; CREATE TABLE tab2( tab2_id varchar(50) ); 创建触发器： delimiter $$ mysql> DROP TRIGGER IF EXISTS tab1_after_trigger; Query OK, 0 rows affected, 1 warning (0.00 sec) CREATE TRIGGER tab1_after_trigger AFTER INSERT ON tab1 FOR EACH ROW BEGIN insert into tab2(tab2_id) values(new.tab1_id); END delimiter ; mysql> select * from tab1; Empty set (0.01 sec) mysql> select * from tab2; Empty set (0.00 sec) 向tab1中插入一条数据： mysql> insert into tab1 values(‘yang‘); Query OK, 1 row affected (0.00 sec) mysql> select * from tab1; +---------+ | tab1_id | +---------+ | yang | +---------+ 1 row in set (0.00 sec) mysql> select * from tab2; +---------+ | tab2_id | +---------+ | yang | +---------+ 1 row in set (0.00 sec) example 3： 创建一个触发器，当student1表有一个更新操作的时候触发更新update_student1表 创建student1表： mysql> create table student1( -> student_id int auto_increment primary key,not null, -> student_name varchar(30) not null, -> student_sex enum(‘f‘,‘m‘) -> ); Query OK, 0 rows affected (0.01 sec) mysql> desc student1; +--------------+---------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +--------------+---------------+------+-----+---------+----------------+ | student_id | int(11) | NO | PRI | NULL | auto_increment | | student_name | varchar(30) | NO | | NULL | | | student_sex | enum(‘f‘,‘m‘) | YES | | NULL | | +--------------+---------------+------+-----+---------+----------------+ 3 rows in set (0.00 sec) mysql> insert into student1 values -> (1,‘book‘,‘m‘), -> (2,‘robin‘,‘m‘), -> (3,‘alice‘,‘f‘) -> ; Query OK, 3 rows affected (0.00 sec) Records: 3 Duplicates: 0 Warnings: 0 创建update_student1表： mysql> create table update_student1( -> update_record int auto_increment primary key not null, -> student_id int not null, -> update_date date -> ); Query OK, 0 rows affected (0.01 sec) mysql> desc update_student1; +---------------+---------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +---------------+---------+------+-----+---------+----------------+ | update_record | int(11) | NO | PRI | NULL | auto_increment | | student_id | int(11) | NO | | NULL | | | update_date | date | YES | | NULL | | +---------------+---------+------+-----+---------+----------------+ 3 rows in set (0.01 sec) mysql> insert into student1 values -> (1,‘book‘,‘m‘), -> (2,‘robin‘,‘m‘), -> (3,‘alice‘,‘f‘) -> ; Query OK, 3 rows affected (0.00 sec) Records: 3 Duplicates: 0 Warnings: 0 delimiter $$ create trigger student_update_trigger before update on student1 for each row begin if new.student_id!=old.student_id then #如果st8udent1表中的student_id和旧的student_id不一样，就触发更新update_student1表；也就是说student1中的student_id变了，update_student1表中的student_id也会被触发更新； update update_student1 set student_id=new.student_id where student_id=old.student_id; end if; end$$ delimiter ; mysql> create trigger student1_update_trigger before update -> on student1 for each row -> begin -> if new.student_id!=old.student_id then -> update update_student1 -> set student_id=new.student_id -> where student_id=old.student_id; -> end if -> ; -> end$$ Query OK, 0 rows affected (0.01 sec) mysql> delimiter ; 再创建一个删除表id的触发器： mysql> delimiter $$ mysql> create trigger student1_delete_trigger before delete -> on student1 for each row -> begin -> delete from update_student1 -> where student_id=old.student_id; -> end$$ Query OK, 0 rows affected (0.01 sec) 修改student1表中的student_id字段，验证触发器： mysql> update student1 set student_id=101 where student_name=‘book‘; Query OK, 1 row affected (0.01 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> select * from student1; +------------+--------------+-------------+ | student_id | student_name | student_sex | +------------+--------------+-------------+ | 2 | robin | m | | 3 | alice | f | | 101 | book | m | +------------+--------------+-------------+ 3 rows in set (0.01 sec) mysql> select * from update_student1; +---------------+------------+-------------+ | update_record | student_id | update_date | +---------------+------------+-------------+ | 1 | 101 | 2017-04-06 | | 2 | 2 | 2017-04-06 | | 3 | 3 | 2017-04-06 | +---------------+------------+-------------+ 3 rows in set (0.00 sec) 可以发现update_student1表中的student_id字段也改变了
还没有写完，待续。。。。。。。。。。。
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