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SQL--NOtes

  🔵 SQL Learning Notes 🟦 Day 1 – Introduction to SQL 🟢 What is SQL? SQL (Structured Query Language) is a language used to communicate with relational databases. 🟨 Uses of SQL Query Data Update Data Delete Data Alter Data 🟨 Important Terminology Term Also Known As Column Field, Attribute Row Record, Tuple 🟨 Schema vs Database ✅ MySQL Schema and Database are the same. ✅ MS SQL Server & PostgreSQL Schema acts as a namespace within a database. 🟦 Day 2 – SQL Query Execution Order 🟨 Execution Order FROM and JOIN WHERE GROUP BY HAVING ORDER BY SELECT TOP 🟨 Important Concepts Aggregated Values Non-Aggregated Values DISTINCT = Unique Values ASC = Lowest to Highest ⬆️ DESC = Highest to Lowest ⬇️ 🟦 Day 3 – SQL Commands 🟢 DQL (Data Query Language) SELECT 🟠 DDL (Data Definition Language) CREATE DROP ALTER 🟣 DML (Data Manipulation Language) INSERT UPDATE DELETE ⭐ Shortcuts 🟣 DML = IUD 🟠 DDL = CDA 🟨 Best Practice (INSERT) INSERT INTO schema_name.table_name (column1, column...
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 Here’s the complete explanation with SQL queries, outputs, and an extra "Explain" column to make it clearer. 1️⃣ Using BETWEEN (Inclusive) SELECT * FROM employees WHERE experience_years BETWEEN 3 AND 7; ✅ Includes employees with 3, 4, 5, 6, and 7 years of experience. Output Example: employee_id name experience_years Explain 101 Alice 3 Included (3 is in range) 102 Bob 4 Included (between 3 and 7) 103 Carol 5 Included (between 3 and 7) 104 David 6 Included (between 3 and 7) 105 Eve 7 Included (7 is in range) 2️⃣ Using >= and <= (Inclusive, Explicit Condition) SELECT * FROM employees WHERE experience_years >= 3 AND experience_years <= 7; ✅ Same result as BETWEEN , but more flexible for modifications. Output Example: employee_id name experience_years Explain 101 Alice 3 Included (3 is in range) 102 Bob 4 Included (between 3 and 7) 103 Carol 5 Included (between 3 and 7) 104 Da...
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ORDER BY, GROUP BY, HAVING, and WHERE clauses

 Sure! Let's start by creating a sample table and then go through ORDER BY , GROUP BY , HAVING , and WHERE clauses in detail with 10 examples . Step 1: Create a Sample Table We will create an employees table to work with. CREATE TABLE employees ( id INT PRIMARY KEY, name VARCHAR(50), department VARCHAR(50), salary INT, experience INT ); Step 2: Insert Sample Data INSERT INTO employees (id, name, department, salary, experience) VALUES (1, 'Alice', 'HR', 60000, 5), (2, 'Bob', 'IT', 75000, 3), (3, 'Charlie', 'IT', 65000, 7), (4, 'David', 'Finance', 50000, 2), (5, 'Eve', 'Finance', 70000, 6), (6, 'Frank', 'IT', 80000, 8), (7, 'Grace', 'HR', 45000, 4), (8, 'Hank', 'IT', 90000, 9), (9, 'Ivy', 'Finance', 60000, 3), (10, 'Jack', 'HR', 55000, 6); Step 3: Understanding Clauses 1. WHERE Clause Filters...
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🖥️☁️Deploying a Personal Website on AWS EC2 with Apache

  Deploying a Personal Website on AWS EC2 with Apache Introduction Hosting a personal website on AWS EC2 using Apache is a great way to showcase your portfolio, resume, or blog. This guide walks you through setting up an Ubuntu EC2 instance, installing Apache, deploying a static website, and customizing your content. Step 1: Launch an EC2 Instance Sign in to AWS Console and navigate to the EC2 Dashboard . Click "Launch Instance" and configure: AMI: Ubuntu (Latest LTS) Instance Type: t2.micro (Free Tier eligible) Security Group: Allow SSH (22), HTTP (80), and HTTPS (443) Key Pair: Download the .pem file for SSH access. Launch the instance and note the Public IP/DNS . Step 2: Connect to EC2 via SSH Use the command below to access your instance: ssh -i "your-key.pem" ubuntu@your-public-ip Replace your-key.pem with your key file and your-public-ip with the EC2 instance's public IP. Step 3: Install Apache Web Server Update packages an...
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🖥️☁️AWS SQS and SNS: A Complete Guide to Messaging Services

  AWS SQS and SNS: A Complete Guide to Messaging Services Introduction AWS provides two powerful messaging services, Simple Queue Service (SQS) and Simple Notification Service (SNS) , for building scalable, decoupled, and event-driven applications. While SQS is a fully managed queuing service that enables asynchronous communication, SNS is a pub/sub messaging service for sending notifications and alerts. AWS SQS (Simple Queue Service) What is AWS SQS? AWS SQS is a message queuing service that allows components of a distributed application to communicate asynchronously. It ensures reliable message delivery between services, even if they are running at different speeds. Key Features of AWS SQS Fully Managed : AWS handles scaling and availability. Decoupling : Separates application components for better scalability. FIFO & Standard Queues : Ensures message ordering when needed. At-least-once Delivery : Guarantees message delivery. Dead-letter Queues (DLQ) : Stores f...
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🖥️☁️AWS SQS and SNS: A Complete Guide to Messaging Services

  AWS SQS and SNS: A Complete Guide to Messaging Services Introduction AWS provides two powerful messaging services, Simple Queue Service (SQS) and Simple Notification Service (SNS) , for building scalable, decoupled, and event-driven applications. While SQS is a fully managed queuing service that enables asynchronous communication, SNS is a pub/sub messaging service for sending notifications and alerts. AWS SQS (Simple Queue Service) What is AWS SQS? AWS SQS is a message queuing service that allows components of a distributed application to communicate asynchronously. It ensures reliable message delivery between services, even if they are running at different speeds. Key Features of AWS SQS Fully Managed : AWS handles scaling and availability. Decoupling : Separates application components for better scalability. FIFO & Standard Queues : Ensures message ordering when needed. At-least-once Delivery : Guarantees message delivery. Dead-letter Queues (DLQ) : Stores f...
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🖥️☁️AWS EMR (Elastic MapReduce): A Comprehensive Guide

  AWS EMR (Elastic MapReduce): A Comprehensive Guide Introduction AWS EMR (Elastic MapReduce) is a cloud-based big data processing service that simplifies running large-scale distributed data processing jobs using open-source frameworks like Apache Spark, Hadoop, Hive, and Presto. It is designed to handle petabyte-scale data efficiently with cost-effective and auto-scalable clusters. Key Features of AWS EMR Scalability : Automatically scales clusters based on workload. Cost-Effective : Uses EC2 Spot Instances to reduce costs. Integration : Supports S3, DynamoDB, Redshift, and more. Managed Service : AWS handles cluster provisioning and management. Security : Integrated with IAM roles, encryption, and VPC. Flexibility : Supports multiple frameworks like Spark, Hadoop, Hive, Presto. AWS EMR Architecture AWS EMR follows a master-worker architecture: Master Node : Manages cluster, schedules jobs, and monitors tasks. Core Nodes : Executes tasks and stores data on HDFS. ...
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