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Lessons (40)

• SQL Language, Identifiers & Data Types

  Interview answers for DDL/DML/DCL, generated IDs, UNION, static/dynamic SQL and CHAR/VARCHAR. Covers PDF questions …

• SQL Interview Query Drills

  … Covers PDF questions 23, 25 and 26. ![SQL drill workflow: define grouping, compute an aggregate, then filter with …

• SQL vs NoSQL Databases

  … tables, rows, relationships sql CREATE TABLE customers ( id BIGSERIAL PRIMARY KEY, email TEXT NOT NULL UNIQUE, name TEXT …

• AWS Messaging: Queues, Topics and Events

  Use SQS to hold work, SNS to fan out notifications, and EventBridge to route events without tightly coupling …

• L — Liskov Substitution Principle

  … Square extends Rectangle In maths, a square is a rectangle. So inheritance seems natural: js class Rectangle { setWidth …

• Event-Driven Patterns, Step Functions and Reliable Lambdas

  … billing] -- L1[Lambda billing] T -- Q2[SQS: email] -- L2[Lambda email] T -- Q3[SQS: analytics] -- L3[Lambda analytics …

• Train Your First Model from Scratch

  … 4. Calculate gradients: estimate how changing each parameter changes mean squared error. 5. Update: subtract the learning rate …

• Database Indexing & Transactions

  … by country, then city, then age. sql CREATE INDEX idx people location ON people (country, city, age); Query …

• Python and Math Foundations with Runnable Examples

  … It is a geometric score, not a probability of correctness. python from math import sqrt def cosine(left …

• AWS Databases: Choose the Right One

  Choose SQL, key-value, or cache storage by the problem you need to solve, then protect it with …

• AWS Data Pipelines in Plain Language

  … Create a practice database: sql CREATE DATABASE IF NOT EXISTS academy; Then create a table for this simple …

• Cross-Service Data: How to Join Without a Database JOIN

  … Their databases are private implementation details, so Order Service cannot safely run a normal SQL JOIN against User …

• Onion Architecture & Clean vs Hexagonal vs Onion

  … infrastructure, UI, tests Implementations of the interfaces, web framework, DB, external APIs SqlOrderRepository , controllers, EF Core / Prisma mermaid …

• Python Web APIs: FastAPI and Django

  … typed env vars ├── database.py engine + session dependency ├── models.py SQLAlchemy tables ├── schemas.py Pydantic request/response models …

• A WhatsApp OTP Is Only Single Use If You Make It So

  … The unsafe version separates them: sql SELECT ... WHERE ... AND consumed at IS NULL; -- both requests see "unused" -- application …

• Code Smells & Refactoring

  … return Math.PI shape.r 2; case "square": return shape.side 2; } } // ✅ Each shape knows how to compute …

• Serverless Architecture

  … your own DynamoDB, S3, Firebase, Supabase, Auth0/Cognito, SQS, EventBridge A "serverless architecture" usually glues managed services together …

• C4 Architecture Diagrams: Context, Container, Component and Code

  … The adapter, repository and publisher handle the details of Stripe, PostgreSQL and SQS. This makes an important design …

• Debug Latency Like an Investigator

  … Compare before/after traces for the same endpoint and split latency into pool wait, SQL execution and downstream …

• AWS Interview Questions: Clear Answers

  … You need a tested recovery process. Does receiving an SQS message remove it? No. Receiving hides it for …

• GitOps, Progressive Delivery and Observability

  … aws-sqs-queue metadata: queueURL: https://sqs.ap-south-1.amazonaws.com/123456789012/jobs queueLength: "20" awsRegion: ap …

• What to Learn in AI, and in What Order

  … Python is the most common language for model experiments; SQL and basic data visualization are useful too. 2 …

• Structural Patterns: How to Connect Objects

  … Square end subgraph Implementation SVG[SvgRenderer] Canvas[CanvasRenderer] end Circle -- bridge -- SVG Circle -.- Canvas Square -.- SVG Square -.- Canvas …

• Go Concurrency: Goroutines, Channels and Context

  … return } } }() return out } // gen → square → print for v := range square(ctx, gen(ctx, 1, 2, 3)) { fmt.Println …

• Storage Engines & Database Operations

  … the signals behind database reliability. What happens below SQL matters A storage engine decides how rows and indexes …

• L6 Production Debugging Casebook

  … queue wait, database acquisition, SQL, remote call, lock, or GC. 3. Check cron jobs, Kubernetes Jobs, @Scheduled jobs …

• Service Communication: Sync vs Async

  … messaging and events A service publishes a message to a broker (Kafka, RabbitMQ, SQS) and moves on. Interested …

• N+1 Queries, Loading & Pagination

  … In production, sample traces rather than logging sensitive SQL values.

• Kafka vs RabbitMQ & the Kafka Ecosystem

  … RabbitMQ (or SQS, BullMQ) for task queues and Kafka as the event backbone. The Kafka ecosystem mermaid flowchart …

• Layered (N-Tier) Architecture

  … No SQL in controllers; no HTTP in services. 2. Dependencies point down: a layer may use the layer …

• Indexes, EXPLAIN & Query Plans

  … checklist Capture slow query fingerprints, not only raw SQL text. Compare p50 and p99. Refresh statistics after data …

• Authentication, Authorization & API Security

  … tokens MFA, rate limiting, short token lifetimes Injection (SQL, NoSQL, command) ' OR 1=1 -- returns every row Parameterised …

• Vertical Slice Architecture & the Modular Monolith

  … simple, direct SQL export async function getOrderHistory(db: Pool, customerId: string) { const { rows } = await db.query( SELECT id …

• TypeScript in Practice

  … Circle Square null) { if (shape === null) return 0; // equality narrowing if ("radius" in shape) return Math.PI shape …

• Concurrency, Resilience & Distributed Workflows

  … Prefer an atomic database statement or a transaction that owns the invariant: sql UPDATE inventory SET available = available …

• AI Evaluation, Safety, and Security

  … Output handling: validate output before using it in SQL, HTML, shell commands, or business actions. Never treat generated …

• Data in Microservices: Sagas & the Outbox Pattern

  … or CDC / Debezium)"] -- K[(Kafka / RabbitMQ)] -- C[Consumers] sql BEGIN; INSERT INTO orders (id, customer id, total cents …

• AWS: Start Here

  … ECS with Fargate Run small event code Lambda SQL database RDS Login Cognito Logs and alarms CloudWatch Security …

• Flash Sale: 10 Million Buyers, No Oversell

  … oversell still needs a durable owner and reconciliation. sql UPDATE inventory SET available = available - 1 WHERE sku = :sku …

• Clean Architecture in Depth

  … no req , no res , no SQL, no Stripe SDK, no JSON. Just the story of placing an order …