MongoDB is one of the most popular NoSQL databases. MongoDB’s decision to store and represent data in a document format means that you can access it from any language, in data structures that are native to that language
The founders decided to build MongoDB as a document database. At the highest level of organization, it is quite similar to a relational database, but as you get closer to the data itself, you will notice a significant change in the way the data is stored. Instead of databases, tables, columns, and rows you have databases, collections, and documents. And in this case document is technically an array.
|SQL Terms/Concepts||MongoDB Terms/Concepts|
|row||document or BSON document|
|table joins||embedded documents and linking|
Specify any unique column or column combination as primary key.
In MongoDB, the primary key is automatically set to the _id field.