In addition to the charts that follow, you might want to consider the Frequently Asked Questions section for a selection of common questions about MongoDB.

The following table presents the various SQL terminology and concepts and the corresponding MongoDB terminology and concepts.

Specify any unique column or column combination as primary key.

In MongoDB, the primary key is automatically set to the _id field.

Tip

For many scenarios, the denormalized data model (embedded documents and arrays) will continue to be optimal for your data and use cases instead of multi-document transactions. That is, for many scenarios, modeling your data appropriately will minimize the need for multi-document transactions.

The following table presents some database executables and the corresponding MongoDB executables. This table is not meant to be exhaustive.

The following table presents the various SQL statements and the corresponding MongoDB statements. The examples in the table assume the following conditions:

• The SQL examples assume a table named people .
• The MongoDB examples assume a collection named people that contain documents of the following prototype:

 
_id: ObjectId("509a8fb2f3f4948bd2f983a0") ,
 
user_id: "abc123",
 
age: 55,
 
status: 'A'
>

The following table presents the various SQL statements related to table-level actions and the corresponding MongoDB statements.

CREATE TABLE people (
 
id MEDIUMINT NOT NULL
 
AUTO_INCREMENT,
 
user_id Varchar(30),
 
age Number,
 
status char(1),
 
PRIMARY KEY (id)
)

Implicitly created on first insertOne() or insertMany() operation. The primary key _id is automatically added if _id field is not specified.

db.people.insertOne( 
 
user_id: "abc123",
 
age: 55,
 
status: "A"
 
> )

However, you can also explicitly create a collection:

db.createCollection("people")

ALTER TABLE people
ADD join_date DATETIME

Collections do not describe or enforce the structure of its documents; i.e. there is no structural alteration at the collection level.

However, at the document level, updateMany() operations can add fields to existing documents using the $set operator.

db.people.updateMany(
 
 < >,
 
< $set: < join_date: new Date( ) > >
)

ALTER TABLE people
DROP COLUMN join_date

Collections do not describe or enforce the structure of its documents; i.e. there is no structural alteration at the collection level.

However, at the document level, updateMany() operations can remove fields from documents using the $unset operator.

db.people.updateMany(
 
 < >,
 
< $unset: < "join_date": "" > >
)