MongoDb 非关系数据库 NoSql 数据库一员， 将数据使用灵活，类JSON形式进行存储。更多：what-is-mongodb

MongoDb is a member of the NoSql， it stores data in flexible, JSON-like documents.

概念 Concepts between SQL and MongoDb

SQL MongoDb
Table Collection
Row Document
Column Field
JOINs Embedded documents, $lookup & $graphLookup
GROUP_BY Aggregation -〉group by

操作 Operation between SQL and MongoDb

SQL MongoDb
INSERT INTO users (user_id, age, status) VALUES ‘bcd001’, 45, ‘A’) db.users.insert({ user_id: ‘bcd001’, age: 45, status: ‘A’})
SELECT * FROM users db.users.find()
UPDATE users SET status = ‘C’ WHERE age > 25 db.users.update( { age: { $gt: 25 } }, { $set: { tatus: ‘C’ } }, { multi: true })
db.start_transaction() cursor.execute(orderInsert, orderData) cursor.execute(stockUpdate, stockData)

db.commit()|s.start_transaction() orders.insert_one(order, session=s) stock.update_one(item, stockUpdate, session=s)s.commit_transaction() （new feature in 4.0 version）|

最大区别 Biggest different between SQL and MongoDb

SQL MongoDb
使用关系型数据库， 需要在数据库中定义对应的表和字段关联。当你需要修改到对应的字段， 必须对数据库进行停机修改，会影响现有的所有数据， 降低应用可用性。In SQL, you pre-define your database schema based on your requirements and set up rules to govern the relationships between fields in your tables.Any changes in schema necessitates a migration procedure that can take the database offline or significantly reduce application performance. 使用MongoDb， 字段 无需在数据库中进行定义，使用代码定义对应的关系。如果需要添加一个新的字段，无需影响其他的document，无需停机进行更新。In MongoDb， Fields is no need to declare the structure of documents to the system – documents are self-describing in Code。If a new field needs to be added to a document,then the field can be created without affecting all other documents in the collection,without updating a central system catalog, and without taking the system offline.
更多的控制在数据库（DBA）， 索引，字段 都需要在数据库进行定义处理More control in Db, Indexes. Filed all controlled in Db side. 更多的控制在代码（开发）， 开发可以在代码中定义对应的索引，字段结构。Less control in Db, more control in Code. Indexes, Fields can controlled in Code side.

参考：mongodb-mysql