[TOC]#补充##join左右连表##上下连表上下连表时，查询出的结果注意列数要相等###union自动去重```select sid,sname from studentsunionselect id,name from teachers```###union all不会去重```select sid,sname from studentsunion allselect sid,sname from students```#视图给某个查询语句设置别名，方便以后使用##创建视图create view 视图名 as SQL```create view v1 as select * from students```##修改视图```alter view 视图名称 as SQL```##删除视图```drop view 视图名称```#触发器当对某张表做增删改时，可以使用触发器自定义关联行为##创建触发器```delimiter //create trigger t1 BEFORE INSERT on student for EACH ROWBEG工N INSERT into teacher(tname) values(NEW.sname);END //delimiter ;```插入数据测试```insert into student(gender,c1ass_id, sname) values(‘女‘,1,‘陈涛‘),(‘女‘,1,‘张根‘‘);NEW,代指新数据，如insert,updateoLD,代指老数据,比如删除，更新时```#函数##内置函数及使用refer:https://dev.mysql.com/doc/refman/5.7/en/functions.htmlrefer:https://dev.mysql.com/doc/refman/5.7/en/date-and-time-functions.html#function_time-format```mysql> SELECT DATE_FORMAT(‘2009-10-04 22:23:00‘, ‘%W %M %Y‘); -> ‘Sunday October 2009‘```##自定义函数#存储过程[返回顶部](#top)