CouchDB或MongoDB是否支持聚合？

Question

CouchDB或MongoDB是否支持聚合？

Answer 1

From MongoDB's point of view, yes.

See: http://www.mongodb.org/display/DOCS/Aggregation

Note there are limitations there (there is work being done to provide greater support for aggregrations, see here ). Typically, you may need to use MapReduce (see Mongo docs here ) especially on larger resultsets.

Answer 2

CouchDB uses map/reduce for this. Aggregation happens during the reduce stage.

For general information on CouchDB's map/reduce system, aka views, see:

• http://guide.couchdb.org/editions/1/en/views.html
• http://wiki.apache.org/couchdb/Introduction_to_CouchDB_views

And for some examples of simulating SQL-style aggregation functions and those CouchDB provides, see:

• http://guide.couchdb.org/editions/1/en/cookbook.html#aggregate
• http://wiki.apache.org/couchdb/Built-In_Reduce_Functions