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Full Stack Web Development Databases & Data Persistence Flashcards
50 question-and-answer cards covering Databases & Data Persistence as it is examined in Full Stack Web Development. 24 of them are printed below, taken from across the deck — no signup, no paywall on the preview.
24 sample cards from the Databases & Data Persistence deck
Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.
What is a self join?
A join in which a table is joined to itself, using table aliases, to compare rows within the same table (e.g., employees to their managers).
What is a subquery in SQL?
A query nested inside another query (in SELECT, FROM, WHERE, etc.) whose result is used by the outer query.
What is the difference between UNION and UNION ALL?
UNION combines result sets and removes duplicate rows; UNION ALL combines them and keeps all duplicates, making it faster.
What is an index in a database and why is it used?
A data structure (often a B-tree) that stores a sorted reference to column values to speed up data retrieval, at the cost of extra storage and slower writes.
What is a transaction in SQL?
A sequence of one or more operations treated as a single atomic unit that either fully commits or fully rolls back, preserving data integrity.
What are window functions used for in advanced SQL?
They perform calculations across a set of rows related to the current row (using OVER) without collapsing rows, enabling running totals, rankings, and moving averages.
Which Node.js library is commonly used to connect to PostgreSQL?
The 'pg' (node-postgres) package.
Which Node.js package is commonly used to connect to MySQL?
mysql2 (or the older mysql package).
What is a connection pool and why use it when connecting Node to a SQL database?
A cache of reusable database connections that reduces the overhead of opening/closing connections per request, improving performance and handling concurrency.
What is a parameterized (prepared) query and why is it important?
A query where values are passed separately from the SQL text using placeholders; it prevents SQL injection and improves performance through query plan reuse.
What is MongoDB?
A document-oriented NoSQL database that stores data as flexible, JSON-like BSON documents organized into collections, with dynamic schemas.
What are the MongoDB equivalents of a SQL table, row, and column?
Collection (table), document (row), and field (column).
What is BSON in MongoDB?
Binary JSON — the binary-encoded serialization format MongoDB uses to store documents, supporting extra types like Date, ObjectId, and binary data.
What is the _id field in a MongoDB document?
The unique primary key of a document; if not provided, MongoDB auto-generates a 12-byte ObjectId for it.
Which MongoDB methods perform CRUD operations?
Create: insertOne/insertMany; Read: find/findOne; Update: updateOne/updateMany/replaceOne; Delete: deleteOne/deleteMany.
How do you find all documents in a MongoDB collection where status equals 'active'?
db.collection.find({ status: "active" })
What is the MongoDB aggregation pipeline?
A framework that processes documents through a sequence of stages (e.g., $match, $group, $sort, $project), each transforming the data and passing results to the next stage.
What do the $match and $group aggregation stages do?
$match filters documents (like WHERE); $group aggregates documents by a specified key and computes accumulated values (like GROUP BY with aggregates).
Why are indexes important in MongoDB?
They allow MongoDB to locate documents efficiently without scanning the whole collection; without them queries perform a full collection scan (COLLSCAN).
What is Mongoose?
An Object Data Modeling (ODM) library for MongoDB and Node.js that provides schema definitions, validation, type casting, middleware, and model-based queries.
What is a Mongoose schema versus a Mongoose model?
A schema defines the structure, fields, types, and validation of documents; a model is a constructor compiled from a schema used to create and query documents in a collection.
What is an ORM, and name two popular SQL ORMs for Node.js.
An Object-Relational Mapper maps database tables to programming objects, letting you query using code instead of raw SQL. Popular Node.js examples: Sequelize and Prisma (also TypeORM).
What is one key advantage and one disadvantage of using an ORM?
Advantage: faster development with cleaner, database-agnostic, injection-safe code. Disadvantage: performance overhead and less control over complex/optimized queries.
How are databases typically connected to APIs in a backend application?
The API server uses a database driver or ORM/ODM to open a (pooled) connection, then route handlers execute queries within request handling and return the results as JSON responses, with credentials kept in environment variables.
What this deck covers
The Databases & Data Persistence deck follows the Full Stack Web Development Databases & Data Persistence syllabus — 4 chapters and 13 topics — so questions land on material that is genuinely examinable rather than trivia around it. That works out to roughly 12.5 cards per chapter.
Answers are written to be recallable, not just readable — averaging about 134 characters, which is long enough to carry the reasoning and short enough to say out loud.
A deck like this earns its keep on the second and third pass. Read the syllabus first so you know the shape of the subject, then use the cards to find the specific facts that have not stuck.
Databases & Data Persistence flashcards FAQ
How many Databases & Data Persistence flashcards are in this Full Stack Web Development deck?
50 cards. This page previews 24 of them, sampled evenly across the deck so you can judge the difficulty before installing anything.
Are these Full Stack Web Development flashcards free?
Yes. The preview here is free to read with no signup, and the full 50-card deck is free inside the Examius app.
What do the Databases & Data Persistence cards cover?
They follow the Full Stack Web Development Databases & Data Persistence syllabus — 4 chapters and 13 topics — so the questions track what is actually examinable.
How should I use these flashcards?
Read the syllabus first so you know the shape of the subject, then drill the deck. Examius schedules each card with spaced repetition, so cards you keep missing come back sooner and ones you know drift further apart.