MongoDB select count(distinct x) on an indexed column - count unique results for large data sets

Question

I have gone through several articles and examples, and have yet to find an efficient way to do this SQL query in MongoDB (where there are millions of rows documen

Answer 1

Following solution worked for me

db.test.distinct('user'); [ "alex", "England", "France", "Australia" ]

db.countries.distinct('country').length 4