如何实现mysql数据库的异地访问

<bean id="dataSource" class="com.alibaba.druid.pool.DruidDataSource" init-method="init" destroy-method="close">

<property name="driverClassName" value="com.mysql.jdbc.Driver" />

<property name="url" value="jdbc:mysql://改成自己要连接数据库的ip地址,和数据库名" />

<property name="username" value="name" />

<property name="password" value="pwd" />

1、where型子查询

（把内层查询结果当作外层查询的比较条件）

#不用order by 来查询最新的商品

select goods_id,goods_name from goods where goods_id = (select max(goods_id) from goods)

#取出每个栏目下最新的产品(goods_id唯一)

select cat_id,goods_id,goods_name from goods where goods_id in(select max(goods_id) from goods group by cat_id)

2、from型子查询

(把内层的查询结果供外层再次查询)

#用子查询查出挂科两门及以上的同学的平均成绩

思路：

#先查出哪些同学挂科两门以上

select name,count(*) as gk from stu where score <60 having gk >=2

#以上查询结果，我们只要名字就可以了，所以再取一次名字

select name from (select name,count(*) as gk from stu having gk >=2) as t

#找出这些同学了，那么再计算他们的平均分

select name,avg(score) from stu where name in (select name from (select name,count(*) as gk from stu having gk >=2) as t) group by name

3、exists型子查询

（把外层查询结果拿到内层，看内层的查询是否成立）

#查询哪些栏目下有商品，栏目表category,商品表goods

select cat_id,cat_name from category where exists(select * from goods where goods.cat_id = category.cat_id)

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