mysql组的结果超过1个相同的数据

I use function group_by in mysql, but in big data 116000 record when I run this sintax there is more than 1 same data. What should I do ??

SELECT fiedl1, field2, field3
 FROM table
GROUP BY field2
ORDER BY 'field2' ASC

field1|field2|field3
1     |you   |a
2     |you   |b
3     |you   |c
4     |you    |d
5 ...etc

result

field1|field2|field3
1     |you   |a
2     |you   |b

Best practice is to use group by on all fields, or agregate functions, for example

SELECT fiedl1, field2, field3 FROM table GROUP BY fiedl1, field2, field3 ORDER BY field2 ASC

OR

SELECT sum(fiedl1), field2, avg(field3) FROM table GROUP BY field2 ORDER BY field2 ASC