场景一，数据表自动备份（多个数据表字段同步等），使用触发器。如updatelog记录对资源的所有操作日志，reslastlog记录资源最后操作的日志信息。同步方式实现如下：
//创建表 DROP TABLE IF EXISTS updatelog; CREATE TABLE `updatelog` ( `id` int(11) NOT NULL AUTO_INCREMENT, `resourceid` int(11) DEFAULT NULL, `log` text, `createtime` datetime DEFAULT NULL, PRIMARY KEY (`id`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 //必须指定主键或unique，不然无法replace DROP TABLE IF EXISTS reslastlog; CREATE TABLE `reslastlog` ( `resourceid` int(11) NOT NULL DEFAULT '0', `log` text, `updatetime` datetime DEFAULT NULL, PRIMARY KEY (`resourceid`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 //创建触发器 DROP TRIGGER IF EXISTS t_afterinsert_on_updatelog; delimiter // CREATE TRIGGER t_afterinsert_on_updatelog AFTER INSERT ON updatelog FOR EACH ROW BEGIN replace into reslastlog(resourceid,log,updatetime) values(new.resourceid, new.log, new.createtime); END; // delimiter ; DROP TRIGGER IF EXISTS t_afterdelete_on_updatelog; delimiter // CREATE TRIGGER t_afterdelete_on_updatelog AFTER DELETE ON updatelog FOR EACH ROW BEGIN delete from reslastlog where resourceid=old.resourceid; END; // delimiter ; //测试 insert into updatelog(resourceid, log, createtime) values(1, "version 1-0",now()); insert into updatelog(resourceid, log, createtime) values(1, "version 1-1",now()); insert into updatelog(resourceid, log, createtime) values(2, "version 2-2",now()); delete from updatelog where resourceid = 2; //触发器相关操作 mysql> show triggers; +----------------------------+--------+-----------+--------------------------------------------------------------------------------------------------------------------+--------+---------+----------+----------------+----------------------+----------------------+--------------------+ | Trigger | Event | Table | Statement | Timing | Created | sql_mode | Definer | character_set_client | collation_connection | Database Collation | +----------------------------+--------+-----------+--------------------------------------------------------------------------------------------------------------------+--------+---------+----------+----------------+----------------------+----------------------+--------------------+ | t_afterinsert_on_updatelog | INSERT | updatelog | BEGIN replace into reslastlog(resourceid,log,updatetime) values(new.resourceid, new.log, new.createtime); END | AFTER | NULL | | root@localhost | latin1 | latin1_swedish_ci | latin1_swedish_ci | | t_afterdelete_on_updatelog | DELETE | updatelog | BEGIN delete from reslastlog where resouceid=old.resourceid; END | AFTER | NULL | | root@localhost | latin1 | latin1_swedish_ci | latin1_swedish_ci | +----------------------------+--------+-----------+--------------------------------------------------------------------------------------------------------------------+--------+---------+----------+----------------+----------------------+----------------------+--------------------+ 2 rows in set (0.00 sec) drop trigger t_afterinsert_on_updatelog;
场景二，用户定义函数或者存储过程实现简单的后台数据运算。示例如下：
//用户定义函数 //创建资源基本信息表 CREATE TABLE `baseinfo` ( `id` int(11) DEFAULT NULL, `content` text ) ENGINE=MyISAM DEFAULT CHARSET=latin1; insert into baseinfo values(1,"one"); insert into baseinfo values(2,"two"); insert into baseinfo values(3,"three"); //创建每日资源pv表 CREATE TABLE `dayinfo` ( `id` int(11) DEFAULT NULL, `pv` int(11) DEFAULT NULL, `day` date DEFAULT NULL ) ENGINE=MyISAM DEFAULT CHARSET=latin1; insert into dayinfo values(1,10,"2014-10-01"); insert into dayinfo values(1,12,"2014-10-02"); insert into dayinfo values(1,16,"2014-10-03"); insert into dayinfo values(2, 30, "2014-10-02"); 查询资源指定时段降序排列 mysql> select baseinfo.id as id, content, sum(pv) as totalpv from baseinfo,dayinfo where baseinfo.id=dayinfo.id and day>="2014-10-02" and day<="2014-10-03" group by id order by totalpv desc; +------+---------+---------+ | id | content | totalpv | +------+---------+---------+ | 2 | two | 30 | | 1 | one | 28 | +------+---------+---------+ 上面的sql语法非常复杂，如果用UDF会方便简洁很多。 1，查看用户定义函数功能是否开启，ON为开启 show variables like '%func%'; 2，如果是OFF，则执行下面的操作 set global log_bin_trust_function_creators=1; 3，创建用户定义函数 delimiter $$ CREATE FUNCTION getTotalPV(targetid int,dayfrom date,dayto date) RETURNS int begin declare totalpv int default 0; set totalpv=(select sum(pv) from dayinfo where id = targetid and day>=dayfrom and day<=dayto); if totalpv is null then set totalpv = 0; end if; return totalpv; end$$ delimiter ; mysql> select id, content, getTotalPV(id, "2014-10-02", "2014-10-03") as totalpv from baseinfo order by totalpv desc; +------+---------+---------+ | id | content | totalpv | +------+---------+---------+ | 2 | two | 30 | | 1 | one | 28 | | 3 | three | 0 | +------+---------+---------+ 4，查看udf定义show create function getTotalPV; //存储过程 drop procedure if exists getjson; delimiter $$ create procedure getjson ( str1 varchar(1024), str2 varchar(1024), str3 varchar(1024), str4 varchar(1024) ) begin if str1 is NULL then set str1=""; end if; if str2 is NULL then set str2=""; end if; if str3 is NULL then set str3=""; end if; if str4 is NULL then set str4=""; end if; select CONCAT("[",str1,",",str2,",",str3,",",str4,"]") as jsonstr; end;$$ delimiter ; mysql> call getjson("a","b","c","d"); +-----------+ | jsonstr | +-----------+ | [a,b,c,d] | +-----------+ 1 row in set (0.00 sec)
场景三：mysql调用外部应用程序（如表有数据更新后，通过触发器调用外部应用程序执行任务）
1.lib_mysqludf_sys简介 mysql中没有执行外部命令的函数，要调用外部的命令，可以通过开发MySQL UDF来实现，lib_mysqludf_sys 就是一个实现了此功能的UDF库。 下载地址：https://github.com/mysqludf/lib_mysqludf_sys 2.使用方法 2.1 安装部署(需要安装mysql-devel) a) lib_mysqludf_sys.so复制到mysql/lib/plugin目录下。 b) 在mysql中创建函数(根据需要选取)： Drop FUNCTION IF EXISTS lib_mysqludf_sys_info; Drop FUNCTION IF EXISTS sys_get; Drop FUNCTION IF EXISTS sys_set; Drop FUNCTION IF EXISTS sys_exec; Drop FUNCTION IF EXISTS sys_eval; Create FUNCTION lib_mysqludf_sys_info RETURNS string SONAME 'lib_mysqludf_sys.so'; Create FUNCTION sys_get RETURNS string SONAME 'lib_mysqludf_sys.so'; Create FUNCTION sys_set RETURNS int SONAME 'lib_mysqludf_sys.so'; Create FUNCTION sys_exec RETURNS int SONAME 'lib_mysqludf_sys.so'; Create FUNCTION sys_eval RETURNS string SONAME 'lib_mysqludf_sys.so'; 2.2 使用此函数 例：在select语句调用mkdir命令 Select sys_exec('mkdir -p /home/user1/aaa') 例：在触发器中调用外部的脚本(脚本需要可执行权限) Create TRIGGER trig_test AFTER Insert ON <table1> FOR EACH ROW BEGIN DECLARE ret INT; Select sys_exec('/home/user1/test.sh') INTO ret; END