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🔹 Basic: What is MongoDB? How does it differ from SQL?
MongoDB is a NoSQL database that stores data in flexible, JSON-like documents. Unlike SQL, which uses tables and rows, MongoDB uses collections and documents, making it more scalable and suitable for unstructured data.
🔹 Intermediate: How does indexing work? Explain $lookup vs. $unwind.
Indexing in MongoDB improves query performance by creating indexes on fields. The `$lookup` operator performs a left outer join between two collections, while `$unwind` deconstructs an array field, creating a separate document for each element.
🔹 Advanced: What is sharding? How does MongoDB ensure ACID compliance?
Sharding is a method for distributing data across multiple servers to handle large datasets. MongoDB ensures ACID compliance through features like multi-document transactions and snapshot isolation.
Practice Verified Codes and Commands:
1. Basic MongoDB Commands:
<h1>Start MongoDB server</h1> mongod <h1>Connect to MongoDB shell</h1> mongo <h1>Show databases</h1> show dbs <h1>Switch to a database</h1> use myDatabase
2. Indexing Example:
[javascript]
// Create an index on the “name” field
db.collection.createIndex({ name: 1 });
// Query using the index
db.collection.find({ name: “John” }).explain(“executionStats”);
[/javascript]
3. $lookup and $unwind Example:
[javascript]
// $lookup example
db.orders.aggregate([
{
$lookup: {
from: “customers”,
localField: “customerId”,
foreignField: “_id”,
as: “customerDetails”
}
}
]);
// $unwind example
db.orders.aggregate([
{ $unwind: “$items” }
]);
[/javascript]
4. Sharding Commands:
<h1>Enable sharding on a database</h1>
sh.enableSharding("myDatabase");
<h1>Shard a collection</h1>
sh.shardCollection("myDatabase.myCollection", { shardKey: 1 });
What Undercode Say:
MongoDB is a powerful NoSQL database that offers flexibility and scalability for modern applications. Understanding its core concepts, such as indexing, aggregation pipelines, and sharding, is crucial for database administrators and developers. Indexing enhances query performance, while `$lookup` and `$unwind` are essential for complex data manipulations. Sharding allows MongoDB to handle large datasets efficiently by distributing data across multiple servers. Additionally, MongoDB’s ACID compliance ensures data integrity, making it a reliable choice for transactional applications.
For further reading, explore MongoDB’s official documentation:
To practice MongoDB commands, use the MongoDB shell or MongoDB Compass for a graphical interface. Familiarize yourself with Linux commands like mongod, mongo, and `systemctl` to manage MongoDB services effectively. For Windows, use PowerShell commands like `Start-Service` and `Stop-Service` to control MongoDB processes.
By mastering these concepts and commands, you can confidently tackle MongoDB-related interview questions and excel in your database management tasks.
References:
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