Blog

In the previous tutorial, you learned about interfaces and generics. Now let’s learn about error handling. Every program needs to handle errors. Kotlin gives you several tools for this, from traditional try/catch to the modern Result type. In this tutorial, you will learn: try/catch/finally try as an expression Custom exceptions The Result type (runCatching, getOrElse, map, fold) Sealed classes for errors Error handling patterns and best practices try/catch/finally The try/catch block catches exceptions. finally always runs, even after an exception. ...

In the previous tutorial, you learned about sealed classes, enum classes, and value classes. Now let’s learn about interfaces, generics, and type constraints. These features let you write flexible, reusable code while keeping type safety. In this tutorial, you will learn: Interfaces and multiple inheritance Generics with <T> Type constraints with where Variance — in and out Star projection * Reified type parameters Interfaces An interface defines a contract. Classes that implement the interface must provide the required functions and properties. ...

In the previous tutorial, you learned about scope functions. Now let’s learn about three important types in Kotlin: enum classes, sealed classes, and value classes. Each one solves a different problem, and knowing when to use which will make your code better. In this tutorial, you will learn: Enum classes — fixed set of constants Sealed classes — restricted hierarchies with different data Sealed interfaces — multiple inheritance with sealed types Value classes — type safety without runtime overhead When to use which Enum Classes An enum class defines a fixed set of constants. Every value is known at compile time. ...

In the previous tutorial, you learned about lambdas and higher-order functions. Now let’s learn about extension functions and properties. Extensions let you add new functions and properties to existing classes without modifying them. This is one of Kotlin’s best features. You can add a toSlug() function to String or a secondOrNull() function to List — without changing the original class. In this tutorial, you will learn: Extension functions Practical extensions like String.toSlug() and List.secondOrNull() Extension properties Extensions on nullable types Companion object extensions Generic extensions Extension Functions An extension function adds a new function to an existing class. The class you extend is called the “receiver.” ...

In the previous tutorial, you learned about collections. Now let’s learn about lambdas and higher-order functions. These are some of the most powerful features in Kotlin. A lambda is a function without a name. You already used lambdas with filter, map, and other collection functions. In this tutorial, you will learn how they work in depth. In this tutorial, you will learn: Lambda syntax and the it keyword Trailing lambdas Function types like (Int) -> String Higher-order functions (functions that take or return functions) Function references Closures Inline functions Lambda Syntax A lambda is written between curly braces { }. The arrow -> separates the parameters from the body. ...

In the previous tutorial, you learned about classes. Now let’s learn about collections — one of the most important topics in Kotlin. You will use collections in almost every program you write. Kotlin’s collections are powerful and expressive. You can filter, transform, group, and combine data with just a few lines of code. In this tutorial, you will learn: List, MutableList, Set, and Map filter, map, flatMap groupBy, sortedBy reduce and fold zip and associate Chaining operations together List A List is an ordered collection. listOf creates a read-only list. mutableListOf creates a list you can change. ...

One AI agent is powerful. But what if you had a team of AI agents — each specialized in a different job — working together on the same project? That is what multi-agent AI systems do. And they are changing how software gets built in 2026. What is a Multi-Agent System? Instead of one AI assistant that does everything, a multi-agent system splits the work between specialized agents: ┌──────────────┐ │ Architect │ Plans the solution, defines the structure └──────┬───────┘ ↓ ┌──────────────┐ ┌──────────────┐ │ Backend Dev │ │ Frontend Dev │ Build code in parallel └──────┬───────┘ └──────┬───────┘ ↓ ↓ ┌──────────────────────────────────┐ │ QA / Testing │ Runs tests, reports bugs └──────────────────────────────────┘ Each agent has: ...

Bookmark this page. Use Ctrl+F (or Cmd+F on Mac) to find what you need. This cheat sheet covers SQL from basic queries to window functions and performance. Try examples at db-fiddle.com. Last updated: March 2026 SELECT Basics SELECT * FROM users; -- all columns SELECT name, email FROM users; -- specific columns SELECT DISTINCT city FROM users; -- unique values SELECT name AS full_name FROM users; -- column alias SELECT * FROM users LIMIT 10; -- first 10 rows SELECT * FROM users LIMIT 10 OFFSET 20; -- rows 21-30 (pagination) WHERE — Filtering Rows SELECT * FROM users WHERE age > 18; SELECT * FROM users WHERE city = 'Berlin'; SELECT * FROM users WHERE age BETWEEN 18 AND 30; SELECT * FROM users WHERE city IN ('Berlin', 'Munich', 'Hamburg'); SELECT * FROM users WHERE name LIKE 'A%'; -- starts with A SELECT * FROM users WHERE name LIKE '%son'; -- ends with son SELECT * FROM users WHERE name LIKE '%alex%'; -- contains alex SELECT * FROM users WHERE email IS NULL; -- null check SELECT * FROM users WHERE email IS NOT NULL; SELECT * FROM users WHERE age > 18 AND city = 'Berlin'; SELECT * FROM users WHERE age > 65 OR age < 18; SELECT * FROM users WHERE NOT city = 'Berlin'; ORDER BY and LIMIT SELECT * FROM users ORDER BY name; -- ascending (default) SELECT * FROM users ORDER BY age DESC; -- descending SELECT * FROM users ORDER BY city, name; -- multiple columns SELECT * FROM users ORDER BY age DESC LIMIT 5; -- top 5 oldest INSERT, UPDATE, DELETE -- Insert one row INSERT INTO users (name, email, age) VALUES ('Alex', 'alex@example.com', 25); -- Insert multiple rows INSERT INTO users (name, email, age) VALUES ('Sam', 'sam@example.com', 30), ('Jordan', 'jordan@example.com', 22); -- Update UPDATE users SET age = 26 WHERE name = 'Alex'; -- Update multiple columns UPDATE users SET city = 'Munich', age = 27 WHERE id = 1; -- Delete DELETE FROM users WHERE id = 5; -- Delete all rows (use with caution!) DELETE FROM users; -- Faster delete all (resets table) TRUNCATE TABLE users; -- UPSERT — insert or update if exists (PostgreSQL) INSERT INTO users (email, name) VALUES ('alex@example.com', 'Alex') ON CONFLICT (email) DO UPDATE SET name = EXCLUDED.name; -- MySQL equivalent INSERT INTO users (email, name) VALUES ('alex@example.com', 'Alex') ON DUPLICATE KEY UPDATE name = VALUES(name); Warning: Always use WHERE with UPDATE and DELETE. Without it, every row is affected. ...

Welcome to Part 2 of the series. You can now build beautiful single-screen apps. But real apps have many screens — a home screen, a detail screen, a settings screen, a profile screen. Navigation is how you move between them. In this tutorial, you will learn everything about Compose navigation: Setting up navigation Creating screens and routes Type-safe navigation with Kotlin Serialization Passing data between screens Bottom navigation bar Nested navigation graphs Back stack management Best practices This is a long tutorial. Take your time. ...

Every AI coding tool has the same problem: it can read your code, but it can’t access your database. It can’t check your Jira tickets. It can’t read your Slack messages. It can’t query your production logs. Until now. MCP (Model Context Protocol) is a new standard that lets AI tools connect to anything — databases, APIs, file systems, project management tools, and more. It is like a USB-C port for AI. One standard connection that works with everything. ...