MongoDB vs RDBMS — MongoDB Technical Interview Questions & Answers

Documents/collections vs rows/tables terminology mapping.

MongoDB vs RDBMS

  • Simple meaning: RDBMS (MySQL) uses tables and SQL joins. MongoDB uses documents and usually embeds related data.
  • Vocabulary: table ≈ collection, row ≈ document, column ≈ field, JOIN ≈ embed or $lookup.
  • How to choose: fees + attendance with foreign keys → MySQL. Product with varying fields, nested comments → MongoDB.
  • Try this: same student in SQL as columns; in Mongo as one document with marks: [72, 40].
  • Common mistake: “Mongo has no joins.” $lookup exists, but embed is the usual design.
  • Interview tip: Pick one use case for each. Do not say one is always better.

Technical Interview Tip: Table=collection, row=document. Strict money → SQL. Flexible docs → Mongo.

Code Examples for MongoDB vs RDBMS

MongoDB vs RDBMS — working example

// Collection "users" holds BSON documents (JSON-like):
db.users.insertOne({
  name: "Ada",
  email: "ada@example.com",
  age: 36,
  skills: ["Java", "MongoDB"],
  address: { city: "Pune", pin: "411001" }
})
db.users.find({ "address.city": "Pune" })

MongoDB vs RDBMS — mongoDB stores BSON documents in collections — flexible schema, nested fields, rich queries.

How to Explain MongoDB vs RDBMS to an Interviewer

When MySQL instead of Mongo?

Fixed schema, foreign keys, many joins Fees / marks sheets