MySQL触发器

触发器
注意几个问题：
1.begin…end
2.什么条件触发
Insert、Update、Delete
3.什么时候触发：Before、After（i、u、d）
4.触发频率：针对每一行数据触发一次。
5.定义在表上，附着在表上。
6.触发器的begin…end之前的语句的执行效率一定要高，这样资源消耗才小。
7.NEW和OLD：代表的是一行，

触发器的语法：

CREATE
    [DEFINER = { user | CURRENT_USER }]
    TRIGGER trigger_name
    trigger_time trigger_event
    ON tbl_name FOR EACH ROW
    [trigger_order]
    trigger_body

trigger_time: { BEFORE | AFTER }
trigger_event: { INSERT | UPDATE | DELETE }
trigger_order: { FOLLOWS | PRECEDES } other_trigger_name

例子1：在插入之前触发

CREATE TABLE account (acct_num INT, amount DECIMAL(10,2));

DELIMITER $$
CREATE TRIGGER ins_sum BEFORE INSERT ON account
FOR EACH ROW 
begin
SET @sum = @sum + NEW.amount;     --》触发器会被触发三次
end$$
DELIMITER ;

mysql> SET @sum = 0;
Query OK, 0 rows affected (0.00 sec)
mysql> INSERT INTO account VALUES(137,14.98),(141,1937.50),(97,-100.00);
Query OK, 3 rows affected (0.03 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> SELECT @sum AS 'Total amount inserted';
+-----------------------+
| Total amount inserted |
+-----------------------+
|               1852.48 |
+-----------------------+
1 row in set (0.00 sec)
mysql> drop trigger ins_sum;
Query OK, 0 rows affected (0.00 sec)

例子2：在修改之前触发

delimiter $$
CREATE TRIGGER upd_check BEFORE UPDATE ON account
FOR EACH ROW
BEGIN
    IF NEW.amount < 0 THEN    --》某一行，更新后的叫new，更新前叫old
        SET NEW.amount = 0;
    ELSEIF NEW.amount > 100 THEN
        SET NEW.amount = 100;
    END IF;
END$$
delimiter ;

mysql> select * from account;
+----------+---------+
| acct_num | amount  |
+----------+---------+
|      137 |   14.98 |
|      141 | 1937.50 |
|       97 | -100.00 |
+----------+---------+
3 rows in set (0.00 sec)
mysql> update account set amount=-10 where acct_num=137;
Query OK, 1 row affected (0.33 sec)
Rows matched: 1  Changed: 1  Warnings: 0    ---》表示执行了触发器
mysql> select * from account;
+----------+---------+
| acct_num | amount  |
+----------+---------+
|      137 |    0.00 |
|      141 | 1937.50 |
|       97 | -100.00 |
+----------+---------+
3 rows in set (0.00 sec)

mysql> update account set amount=200 where acct_num=137;   
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0
mysql> select * from account;
+----------+---------+
| acct_num | amount  |
+----------+---------+
|      137 |  100.00 |
|      141 | 1937.50 |
|       97 | -100.00 |
+----------+---------+
3 rows in set (0.01 sec)

例子3：更新前把old数据备份到备份表里

create table account_bak as select * from account where 1=2;
delimiter $$
CREATE TRIGGER UPDATE_check BEFORE update ON account
FOR EACH ROW
BEGIN
    insert into account_bak values(OLD.acct_num,OLD.amount);
END$$
delimiter ;

mysql> select * from account;
+----------+---------+
| acct_num | amount  |
+----------+---------+
|      137 |  100.00 |
|      141 | 1937.50 |
|       97 | -100.00 |
+----------+---------+
3 rows in set (0.00 sec)

mysql> select * from account_bak;    --》account_bak表刚开始是空的。
Empty set (0.00 sec)
mysql> update account set amount=200 where acct_num=141;    --》执行update语句
Query OK, 1 row affected (0.34 sec)
Rows matched: 1  Changed: 1  Warnings: 0    --》证明调用了触发器

mysql> select * from account_bak;
+----------+---------+
| acct_num | amount  |
+----------+---------+
|      141     | 1937.50 |
+----------+---------+
1 row in set (0.00 sec)

event调度器
event概念：可以理解为预约计划系统做某些操作。
①一次②周期性执行
周期的开始、周期的结束、每隔多长时间（每分钟、每秒、每天、每个季度、每周…）
通常，指定周期的开始、间隔

event语法：

CREATE
    [DEFINER = { user | CURRENT_USER }]
    EVENT
    [IF NOT EXISTS]
    event_name
    ON SCHEDULE schedule
    [ON COMPLETION [NOT] PRESERVE]
    [ENABLE | DISABLE | DISABLE ON SLAVE]
    [COMMENT 'comment']
    DO event_body;

schedule:（时刻）
    AT timestamp [+ INTERVAL interval] ...    --》从现在开始
  | EVERY interval
    [STARTS timestamp [+ INTERVAL interval] ...]
    [ENDS timestamp [+ INTERVAL interval] ...]

interval:（间隔）
    quantity {YEAR | QUARTER | MONTH | DAY | HOUR | MINUTE |
              WEEK | SECOND | YEAR_MONTH | DAY_HOUR | DAY_MINUTE |
              DAY_SECOND | HOUR_MINUTE | HOUR_SECOND | MINUTE_SECOND}

例子1：

mysql>create table t1(id int,mycol int);
mysql> insert into t1 values(1,1);
Query OK, 1 row affected (0.00 sec):
mysql> insert into t1 values(2,2);
Query OK, 1 row affected (0.01 sec)
mysql> insert into t1 values(3,3);
Query OK, 1 row affected (0.01 sec)      

打开数据库的event执行调度

mysql> show variables like '%event_scheduler%';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| event_scheduler | OFF   |
+-----------------+-------+
1 row in set (0.01 sec)

mysql> set global event_scheduler =1;
Query OK, 0 rows affected (0.00 sec)

重新登录再执行下面的语句：

mysql> show variables like '%event_scheduler%';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| event_scheduler | ON    |
+-----------------+-------+
1 row in set (0.00 sec)    --》证明event调度打开了。

delimiter $$
CREATE EVENT myevent
    ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 1 MINUTE
    DO
begin
      UPDATE t1 SET mycol = mycol + 1;
end$$
delimiter ;

mysql>show events;
/var/log/mysqld.log
2016-01-17T10:40:52.018009Z 10 [Note] Event Scheduler: scheduler thread started with id 10

create table t2(id int auto_increment primary key,t_time datetime);
delimiter $$
CREATE EVENT e_daily
    ON SCHEDULE
      EVERY 1 MINUTE
    COMMENT 'Saves total number of sessions then clears the table each day'
    DO
      BEGIN
        INSERT INTO t2 values (null,current_timestamp);
      END $$
delimiter ;
mysql> select EVENT_NAME,LAST_EXECUTED from information_schema.EVENTS;
+------------+---------------------+
| EVENT_NAME | LAST_EXECUTED|
+------------+---------------------+
| e_daily       |2016-01-17 18:53:09|
+------------+---------------------+
1 row in set (0.00 sec)

mysql> use TENNIS;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> show events G        --》查看events的具体信息
*************************** 1. row ***************************
                  Db: TENNIS
                Name: e_daily
             Definer: root@localhost
           Time zone: Asia/Shanghai
                Type: RECURRING
          Execute at: NULL
      Interval value: 1
      Interval field: MINUTE
              Starts: 2016-01-17 18:52:09
                Ends: NULL
              Status: ENABLED
          Originator: 0
character_set_client: utf8
collation_connection: utf8_general_ci
  Database Collation: utf8_general_ci
1 row in set (0.00 sec)
mysql>