问题一：查询出某个字段所有不重复的数据以及求和？

问题二：查询出所有不重复的数据？

问题三：查询数据中所有某字段重复的记录？

id        name           address

1         a                 shanghai

2         a                 beijing

3         b                 hongkong

4         c                 hunan

5         d                 hubei

解决问题一：

1）、distinct

select distinct name from tablename;--求数据

select count(distinct name) from tablename;--求和

2）、group by

select name from tablename group by name;--求数据

select count(min(id)) from tablename group by name;--求和

select count(max(id)) from tablename group by name;--求和

解决问题二：

select * from tablename where id in(select min(id) from tablenamegroup by name) order by id;

select * from tablename where id in(select max(id)from tablename group by name) order by id;

解决问题三：

select *   from table  where name in        (select name from table group by name having count(name) >1);

注：having count(name) >1 表示相同name列数据出现的次数，大于1就表示重复数据。