MongoDB Summary (ii): Conceptual analysis

The basic concept in MongoDB is a document, a collection, a database

With an example, some concepts in MONGO are more visually understood:

Show DBS shows a list of all data

DB is the display of the current database object or collection

Use test to connect to a specified database

Some database names are reserved and can be accessed directly from these databases with special effects.
Admin

From the perspective of permissions, this is the "root" database. If you add a user to this database, the user automatically inherits permissions from all databases. Some specific server-side commands can only be run from this database, such as listing all databases or shutting down the server.
Local

This data is never copied and can be used to store any collection that is limited to a local single server
Config

When MONGO is used for sharding settings, the Config database is used internally to hold information about the Shard.

The following is a list of terms that RDBMS and MongoDB correspond to:

Areas of demand attention:

MongoDB is case-sensitive;

Keys that begin with the underscore "_" are reserved (not strictly required);

and $ have special meaning and can only be used in certain circumstances;

The collection name cannot begin with system.

MongoDB Data type:

MongoDB Summary (ii): Conceptual analysis