Recursos SQL- materiales educativos

🚀 SQL Roadmap 2026 — Part 2 SQL SELECT Statement & Retrieving Data Now that you understand databases, tables, rows, columns, primary keys, and foreign keys, it's time to learn the most fundamental SQL command: SELECT. Almost every SQL analysis starts with retrieving data. 1️⃣ What is SELECT? SELECT is used to retrieve data from one or more columns in a table. Basic syntax: SELECT column_name FROM table_name; Example: SELECT customer_name FROM customers; 2️⃣ Select Multiple Columns You can retrieve multiple columns by separating them with commas. SELECT customer_id, customer_name, city FROM customers; Result: customer_id | customer_name | city 1 | Rahul | Mumbai 2 | Priya | Delhi 3 | Amit | Pune 3️⃣ Select All Columns Using * If you want every column: SELECT * FROM customers; * means all columns. ⚠️ Interview Tip: Although SELECT * is convenient while exploring data, avoid relying on it in production queries. Prefer selecting only needed columns. 4️⃣ Column Aliases Use AS to give a column a different name in the result. SELECT customer_name AS name, city AS location FROM customers; The original table is not changed. 5️⃣ Aliases Without AS SELECT customer_name name, city location FROM customers; However, using AS is generally clearer for beginners. 6️⃣ Calculations Inside SELECT SELECT product_name, price, price * 0.90 AS discounted_price FROM products; 7️⃣ Arithmetic Operators + Addition, - Subtraction, * Multiplication, / Division SELECT product_name, selling_price, cost_price, selling_price - cost_price AS profit FROM products; 8️⃣ Using Expressions SELECT product_name, quantity, unit_price, quantity * unit_price AS total_value FROM order_items; 9️⃣ DISTINCT Removes duplicate values. SELECT DISTINCT city FROM customers; 🔟 DISTINCT Across Multiple Columns SELECT DISTINCT city, customer_segment FROM customers; 1️⃣1️⃣ Using SELECT With Text SELECT customer_name, 'Active Customer' AS status FROM customers; 1️⃣2️⃣ Combining Columns SELECT first_name, last_name, CONCAT(first_name, ' ', last_name) AS full_name FROM employees; 1️⃣3️⃣ SELECT With a Condition SELECT customer_name, city FROM customers WHERE city = 'Mumbai'; 1️⃣5️⃣ SQL Query Structure At this stage, learn this basic pattern: SELECT column1, column2 FROM table_name; SELECT column1, column2 FROM table_name WHERE condition; 1️⃣6️⃣ A Real-World Example Manager asks: "Show me product name, selling price, cost price, and profit" SELECT product_name, selling_price, cost_price, selling_price - cost_price AS profit FROM products;