发布于 2016-10-22 11:03:33 | 146 次阅读 | 评论: 0 | 来源: 网友投递
Mysql关系型数据库管理系统
MySQL是一个开放源码的小型关联式数据库管理系统,开发者为瑞典MySQL AB公司。MySQL被广泛地应用在Internet上的中小型网站中。由于其体积小、速度快、总体拥有成本低,尤其是开放源码这一特点,许多中小型网站为了降低网站总体拥有成本而选择了MySQL作为网站数据库。
MySQL数据库中查询重复数据
select * from employee group by emp_name having count (*)>1;
Mysql 查询可以删除的重复数据
select t1.* from employee t1 where (t1.emp_name) in (select t4.emp_name from (select t2.emp_name from employee t2 group by t2.emp_name having count(*)>1) t4) and t1.emp_id not in (select t5.emp_id from (select min(t3.emp_id) as emp_id from employee t3 group by t3.emp_name having count(*)>1) t5);
Mysql 删除重复的数据
delete t1 from employee t1 where (t1.emp_name) in (select t4.emp_name from (select t2.emp_name from employee t2 group by t2.emp_name having count(*)>1) t4) and t1.emp_id not in (select t5.emp_id from (select min(t3.emp_id) as emp_id from employee t3 group by t3.emp_name having count(*)>1) t5);