What is MongoDB?

• Simple meaning: MongoDB is a NoSQL database. It stores data as documents (like a JSON object), not as rows in a table.
• Picture: one student is one document: { name: "Asha", roll: 12, marks: 72 }. Many students live in a collection called students. Collections live in a database called college.
• How to start (10 minutes): 1) Install MongoDB Community or create a free Atlas cluster. 2) Open mongosh (or Compass). 3) Run: use college then insert one student then db.students.find().
• SQL map: database → database, table → collection, row → document, column → field. Primary key is _id (Mongo makes it if you skip it).
• When to use it: notes, product catalogs, logs, profiles — data whose shape can change. Prefer MySQL/Postgres when you need strict tables, foreign keys, and lots of joins (fees, marks sheets).
• Common mistake: treating MongoDB like “SQL with no rules”. You still design embed vs reference. Another trap: opening a .js file in the browser — mongosh talks to the database, not Chrome.
• Interview tip: “Document database. Collection of BSON documents. Flexible fields. Query with find({ roll: 12 }).”

  college (database)
     │
     ▼
  students (collection)
     │
     ▼
  { name, roll, marks }

Technical Interview Tip: Say document + collection + _id + one find example.