elasticsearch-DSL aggregation of part of query result. like select * from (select * from table limit 100)

[jacksonxie]

Hi,
ES version: 5.5.2
System: win7
problem:
For SQL: if I want to statistic part of the query result. I can use the SQL with two "select" like:
select count(distinct col_name) from (select * from table limit 100) A group by col_name;
For ES-DSL, how can I reach the same goal. Could any one tell me. thks very much.