✅ SQL Functions 📊🧠

SQL functions are built-in operations used to manipulate, calculate, and transform data. They help in summarizing results, formatting values, and applying logic in queries.

1️⃣ Aggregate Functions
These return a single result from a group of rows.

• COUNT() – Counts rows
SELECT COUNT(*) FROM employees;

• SUM() – Adds values
SELECT SUM(salary) FROM employees WHERE department = 'IT';

• AVG() – Returns average
SELECT AVG(age) FROM customers;

• MAX() / MIN() – Highest or lowest value
SELECT MAX(salary), MIN(salary) FROM employees;

2️⃣ String Functions

• UPPER() / LOWER() – Change case
SELECT UPPER(name), LOWER(city) FROM customers;

• CONCAT() – Join strings
SELECT CONCAT(first_name, ' ', last_name) AS full_name FROM users;

• SUBSTRING() – Extract part of a string
SELECT SUBSTRING(name, 1, 3) FROM products;

• LENGTH() – Length of string
SELECT LENGTH(description) FROM products;

3️⃣ Date Functions

• CURRENT_DATE / NOW() – Current date/time
SELECT CURRENT_DATE, NOW();

• DATE_ADD() / DATE_SUB() – Add or subtract days
SELECT DATE_ADD(hire_date, INTERVAL 30 DAY) FROM employees;

• DATEDIFF() – Difference between dates
SELECT DATEDIFF(end_date, start_date) FROM projects;

• YEAR() / MONTH() / DAY() – Extract parts
SELECT YEAR(order_date), MONTH(order_date) FROM orders;

4️⃣ Mathematical Functions

• ROUND() – Round decimals
SELECT ROUND(price, 2) FROM products;

• CEIL() / FLOOR() – Round up/down
SELECT CEIL(4.2), FLOOR(4.8);

• ABS() – Absolute value
SELECT ABS(balance) FROM accounts;

5️⃣ Conditional Function

• COALESCE() – Returns first non-null value
SELECT COALESCE(phone, 'Not Provided') FROM customers;

• CASE – If/else logic in SQL

  SELECT name,  
    CASE  
      WHEN salary > 50000 THEN 'High'  
      WHEN salary BETWEEN 30000 AND 50000 THEN 'Medium'  
      ELSE 'Low'  
    END AS salary_band  
  FROM employees;
  

🎯 Use These Functions To:
• Summarize data
• Clean and format strings
• Handle nulls
• Calculate time differences
• Add logic into queries

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