This will largely depend on the implementation of the Mongo DB storage plugin. Based on my glimpse at the plugin code [1], it looks like we read all the data from Mongo DB and then aggregation in drill
[1] https://github.com/apache/drill/blob/master/contrib/storage-mongo/src/main/java/org/apache/drill/exec/store/mongo/MongoGroupScan.java On Mon, Oct 2, 2017 at 8:42 AM, Andy <[email protected]> wrote: > Hi, Drill Team > My name is Andy. > Currently, Im considering to use Apache Drill to query and aggregate data > from MongoDB. > > But I really confused how does it work about aggregation. > For example i have this query: > SELECT user,SUM(amount) > FROM sales WHERE type=1 > GROUP BY user > > Then, i have 2 thinking on this: > 1. Drill will use aggregate from MongoDB's api to do GROUP BY > 2. Drill will filter data ( find from Mongo API) then it will do > aggregation by its own way ( such as: collect all matching documents onto > memory & do group by ) > > So, can you help me to understand how it works > Thanks in advanced >
