Beginner

In the previous article, you learned how to read data with SELECT. But a database is not useful if you cannot add, change, or remove data. This article covers the three commands that modify data: INSERT, UPDATE, and DELETE. You will also learn about transactions — a way to make sure your changes are safe. Our Sample Database We continue with the same online bookstore database. If you need to set it up, copy the CREATE TABLE and INSERT statements from the first article. ...

You have data. You need to get answers from it. SQL is the language that does this. Every app you use — social media, banking, shopping — stores data in a database. SQL is how developers read, filter, and organize that data. It has been around since the 1970s, and it is still the most important skill for working with data. What Is SQL? SQL stands for Structured Query Language. It is a language for talking to databases. You write a query, and the database gives you the answer. ...

In the previous tutorial, we learned how to build a Docker image for a single application. But most real applications need more than one service. A web app might need a database. An API might need a cache. A backend might need a message queue. Running each service with docker run and connecting them manually is tedious. Docker Compose solves this. It lets you define all your services in one file and start everything with a single command. ...

In the previous tutorial, we ran containers from pre-built images like ubuntu and nginx. That is useful, but in real projects you need to package your own application into an image. That is what a Dockerfile does. A Dockerfile is a text file with instructions that tell Docker how to build an image. Think of it as a recipe — each line is a step. Your First Dockerfile Let’s create a simple Node.js application and package it with Docker. ...

You write an app. It works on your computer. You send it to a friend. It does not work on their computer. They have a different operating system, a different version of Python, or missing libraries. This is the classic “it works on my machine” problem. Docker solves it. What Is Docker? Docker is a tool that packages your application and everything it needs into a container. A container includes your code, libraries, system tools, and settings. It runs the same way everywhere — on your laptop, your colleague’s laptop, or a server in the cloud. ...

In the previous tutorial, we learned to create a repository, stage files, and make commits. All our work happened on one branch — main. But what if you want to add a new feature without breaking your working code? What if two people need to work on different things at the same time? This is why branches exist. A branch is a separate line of development. You can make changes on a branch without affecting other branches. When you are done, you merge the changes back. ...

Every developer uses Git. It does not matter if you write Python, JavaScript, Rust, or Kotlin. Git tracks your code changes, lets you go back to any previous version, and helps you work with other developers. In this tutorial, you will install Git, create your first repository, and make your first commit. By the end, you will understand how Git tracks changes. What Is Git? Git is a version control system. It saves snapshots of your project over time. Each snapshot is called a commit. ...

These ten concepts appear in almost every Python project. If you know all of them, you can read and write real Python code. If you are missing one, that is the one that trips you up on every project. 1. Variables and Data Types Python infers types automatically. No declaration needed. name: str = "Alex" age: int = 25 score: float = 9.5 active: bool = True nothing = None print(type(name)) # <class 'str'> The four built-in collection types: numbers = [1, 2, 3] # list — ordered, mutable point = (10, 20) # tuple — ordered, immutable tags = {"python", "dev"} # set — unique items user = {"name": "Alex", "age": 25} # dict — key/value pairs Use type() to check the type of any variable at runtime. Use type hints for documentation and IDE support. ...

In the previous tutorial, we created a KMP project and ran it on Android and iOS. Now let’s understand exactly how that project is organized — because once you understand the structure, everything else in KMP makes sense. This is the tutorial that separates developers who struggle with KMP from those who build confidently. Take your time. The Core Idea: Source Sets A KMP project is organized into source sets. Each source set is a collection of Kotlin files that compile to specific platforms. ...

In the previous tutorial, we learned what KMP is and why it matters. Now let’s get our hands dirty — create a real project, understand every file in it, write shared code, and run it on both Android and iOS. This is a long tutorial. Take your time. By the end, you will have a working cross-platform app and understand exactly how every piece fits together. Part 1: Setting Up Your Environment What You Need Tool Required Purpose Android Studio Yes IDE for KMP development (latest stable) Xcode Yes (Mac only) Builds and runs iOS apps JDK 17+ Yes Kotlin compiler depends on it Mac computer For iOS Apple requires Xcode, which only runs on macOS CocoaPods Optional Some KMP libraries need it for iOS If you are on Windows or Linux, you can still write shared code and build the Android app. But you cannot build or run iOS. There is no way around this — Apple controls iOS builds. ...