The golden rules for deciding how to structure your MongoDB data.

Every time you have related data, ask yourself one question:

Goal: Chain multiple operations together — filter, join, calculate — in a single query. Key Idea: The Aggregation Pipeline is a series of stages. Each stage transforms the data and passes it to the next.

Goal: Combine data from two separate collections. Key Idea: MongoDB's equivalent of LEFT OUTER JOIN is the $lookup stage inside an Aggregation Pipeline.

| | SQL JOIN | MongoDB $lookup |

Goal: Query data that lives inside a list (array) within a document. Key Idea: MongoDB searches inside arrays automatically — no extra joins needed.

In a relational database, storing multiple tags for a post requires three tables and a join:

Goal: Return only the fields you need, not the entire document. Key Idea: In MongoDB, .find() takes two arguments — the filter, then the projection.

Goal: Filter results based on status or numerical ranges. Key Idea: MongoDB uses Operators (words starting with $) instead of math symbols.

| SQL | MongoDB Operator | Meaning |

Goal: Look up a single specific record, like a user by their email.

This guide translates common SQL operations into MongoDB (NoSQL) syntax, highlighting the shift from tables and rows to collections and documents.

With a single XAMPP installation, you have 3 options to run multiple PHP versions:

This is the most common use case.