SQL - Introduction to SQL Functions

SQL functions are predefined operations in SQL that help perform calculations, manipulate data, or extract information from tables. They make queries powerful, efficient, and concise.

Why Use SQL Functions?

• To perform calculations on data
• To manipulate text or dates easily
• To summarize data using aggregates
• To simplify complex queries

Types of SQL Functions

1.    Aggregate Functions – Operate on multiple rows, return single value

o   Examples: COUNT(), SUM(), AVG(), MIN(), MAX()

2.    Scalar Functions – Operate on single values, return one value per row

o   Examples: UPPER(), LOWER(), ROUND(), LENGTH()

3.    String Functions – Manipulate text data

o   Examples: CONCAT(), SUBSTRING(), REPLACE()

4.    Date & Time Functions – Work with dates and timestamps

o   Examples: NOW(), CURDATE(), DATEDIFF(), DATE_ADD()

Example

SELECT UPPER(name) AS uppercase_name, COUNT(*) AS total_employees

FROM employees;

• UPPER(name) → converts names to uppercase
• COUNT(*) → counts total rows in employees

Key Points

• Functions can be used in SELECT, WHERE, ORDER BY clauses
• Aggregate functions are often combined with GROUP BY
• Scalar functions help in data formatting and manipulation