Mongo learn plan

subset of whole document in collection (like get several rows in SQL DB) db.tbl.aggregate(pipeline):

                    pipeline = [{$match: {"root_field.nested_fld.nested_fld.target_flg" : target_value}}, {$out: "sam_raw"}]

This like SQL query:

                    create table sam_raw as select * from tbl where target_flg=target_value

Use mongo command db.mycol.update({}, {"$set": {"new_filed" : "new value"}}, {"upsert":"false", "multi" : "true"})
Use pymongo: col.update_many({}, {"$set": {"new_filed" : "new value"}}, upsert = False)

Looks python pipeline syntax with extra double quotation also works for Mongo directly.

Purpose	Mongo	SQL	python: pymongo
Load JSON array	`mongoimport --db mydb --collection mycol /full/path/my.JSONarray --jsonArray`		`def jsonarray_import(raw_path, db_url, db_port, db_name, coll_name): """ Imports JSON array data file raw_path with full path to a mongo collection returns: count of the documents in the new collection """ with open(raw_path, 'r') as f: buff = f.read() payload = json.loads(buff) client = MongoClient(db_url, db_port) db = client[db_name] coll = db[coll_name] coll.remove() coll.insert(payload) return coll.count()`
append one collection to another	`db.this_col.aggregate([{"$merge" : {"into" : "appended_col", "on" : "_id"}}])`	`insert into appended_tbl select * from this_tbl`	pipeline = [{"$merge" : {"into" : "appended_col", "on" : "_id"}}]; this_col.aggregate(pipeline)
Frequency based on fields	`db.txn.aggregate([{$group : {_id : "$root_field.nested_fld.target_fld", num_txn : {$sum : 1}}}])`	`select target_fld, count(*) as num_txn from schema.tbl group by 1`	`pipeline = [{"$group" : {"_id" : "$root_field.nested_fld.target_fld", "num_txn" : {"$sum" : 1}}}]; rst=list(col.aggregate(pipeline))`
	`db.txn.aggregate([{$group : {_id : "$root_field.nested_fld.target_fld", num_txn : {$sum : 1}}}, {$out: "freq_target_fld"}])`	`create table freq_target_fld as select target_fld, count(*) as num_txn from schema.tbl group by 1`	`pipeline = [{"$group" : {"_id" : "$root_field.nested_fld.target_fld", "num_txn" : {"$sum" : 1}}}, {"$out": "freq_target_fld"}]; col.aggregate(pipeline)`
check duplication	NA?
check key field duplication	`pipeline=[ {"$group" : {"_id" : {"fld1" : "$root_field.nested_fld.target_fld1", "fld2" : {"$substr": ["$root_field.nested_fld.target_fld2", 0,10]}, "fld3" : "$root_field.nested_fld.target_fld3", "fld4" : "$root_field.nested_fld.target_fld4", }, "count" : {"$sum" : 1} } }, {"$match": { "count": {"$gt": 1} } }, ] db.txn.aggregate(pipeline)`	`select fld1, fld2, fld3, fld4, count() from schema.tbl group by 1,2,3,4 having count()>1`	`mycol.aggregate(pipeline)`
get subset of documentation: one to one
get subset of documentation: one to multiple