Developer B · Backend

Database concepts

What a database is, why we use one instead of files.

Tables

Rows, columns, data types, NULL.

Primary key

Identity of a row, natural vs surrogate keys.

Foreign key

Referencing another table, cascade behaviour.

Relationships

One-to-one, one-to-many, many-to-many via join tables.

SQL

What SQL is and how a statement is structured.

SELECT

Filtering, ordering, limiting, aggregating.

INSERT

Single and bulk inserts, returning generated keys.

UPDATE

Safe updates, always knowing your WHERE clause.

DELETE

Hard vs soft delete, referential integrity.

JOIN

Inner, left, right and self joins; when each one is right.

Indexes

What an index costs, when it helps, reading a query plan.

Transactions

ACID, isolation levels, deadlocks.

Database migration

Versioned schema change, forward and rollback.

Backup and recovery

Backup strategy, restore drill, point-in-time recovery.

What an API is

Contract between a client and a server.

HTTP basics

Methods, status codes, headers, body.

REST resources

Resource modelling, URL design, idempotency.

JSON payloads

Serialisation, nullability, versioning a payload.

Routing and controllers

Mapping a request to a handler.

Validation

Rejecting bad input at the boundary.

Authentication

Sessions, tokens, refresh flows.

Authorization

Role and ownership checks that cannot be bypassed.

Error handling

Consistent error shape, correct status codes.

Pagination and filtering

Offset vs cursor, stable ordering.

API documentation

OpenAPI, keeping docs true to the code.

Logging and monitoring

Request logs, correlation ids, alerting.

Rate limiting

Protecting an API under load or abuse.

API versioning

Shipping breaking changes without breaking clients.