Add numeric functions

src/data/courses/sql-mastery/chapters/scalar-functions/lessons/numeric-functions.md

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+---
+title: Numeric Functions
+description: Learn how to perform mathematical operations using SQL numeric functions
+order: 120
+type: lesson-challenge
+setup: |
+  ```sql
+  CREATE TABLE sale (
+    sale_id INT,
+    amount INT
+  );
+
+  INSERT INTO sale (sale_id, amount) 
+  VALUES (1, 110), 
+    (2, 320), 
+    (3, 630), 
+    (4, 140), 
+    (5, -150), 
+    (6, 550);
+
+  CREATE TABLE product (
+    product_id INT,
+    price INT
+  );
+
+  INSERT INTO product (product_id, price) VALUES (1, 100), (2, 200), (3, 300), (4, 400), (5, 500);
+  ```
+---
+
+Numeric functions help you perform mathematical calculations and manipulate numeric values. These functions are essential for financial calculations, statistical analysis, and general numeric data processing.
+
+Let's look at some of the common numeric functions in this lesson.
+
+## Rounding Functions
+
+When working with decimal numbers, you often need to round them to a specific number of decimal places. SQL provides several functions for this:
+
+```sql
+-- Round to nearest integer
+SELECT ROUND(3.7);    -- Returns: 4
+SELECT ROUND(3.3);    -- Returns: 3
+
+-- Round to specific decimal places
+SELECT ROUND(3.14159, 2);  -- Returns: 3.14
+
+-- Round up (ceiling)
+SELECT CEILING(3.1);     -- Returns: 4
+
+-- Round down (floor)
+SELECT FLOOR(3.9);    -- Returns: 3
+```
+
+## Absolute Value and Sign
+
+These functions are useful when you need to work with numbers regardless of their sign, or when you need to determine if a number is positive, negative, or zero:
+
+```sql
+-- Get absolute value
+SELECT ABS(-15.7);    -- Returns: 15.7
+
+-- Get sign of number (-1, 0, or 1)
+SELECT SIGN(-15.7);   -- Returns: -1
+SELECT SIGN(0);       -- Returns: 0
+SELECT SIGN(15.7);    -- Returns: 1
+```
+
+## Power and Square Root
+
+For more complex calculations, SQL provides functions for exponents and roots:
+
+```sql
+-- Power function - 2^3
+SELECT POWER(2, 3);   -- Returns: 8
+
+-- Square root
+SELECT SQRT(16);      -- Returns: 4
+```
+
+## Practical Examples
+
+Let's look at some examples using sample tables:
+
+### Order Table
+
+| sale_id | amount |
+| ------- | ------ |
+| 1       | 110    |
+| 2       | 320    |
+| 3       | 630    |
+| 4       | 140    |
+| 5       | -150   |
+| 6       | 550    |
+
+### Calculating Sales Tax
+
+Let's say that we want to add a 10% tax to each order and round the result to 2 decimal places:
+
+```sql
+SELECT
+    sale_id,
+    amount,
+    ROUND(amount * 10 / 100, 2) as tax,
+    ROUND(amount + (amount * 10 / 100), 2) as amount_with_tax
+FROM sale
+WHERE amount > 0; -- ignore refunds
+```
+
+### Handling Negative Values
+
+Sometimes you might need to handle negative values (like refunds) in your financial calculations:
+
+```sql
+SELECT
+    sale_id,
+    amount,
+    ABS(amount) as absolute_amount,
+    CASE
+        WHEN SIGN(amount) = 1 THEN 'Payment'
+        WHEN SIGN(amount) = -1 THEN 'Refund'
+        ELSE 'Zero Transaction'
+    END as transaction_description
+FROM sale;
+```
+
+### Applying Dynamic Discounts
+
+Let's say that we want to apply a 10% discount to products priced at $100 or more, and keep the original price for cheaper products:
+
+```sql
+SELECT
+    product_name,
+    price,
+    CASE
+        WHEN price >= 100 THEN ROUND(price * 0.9, 2)  -- 10% off
+        ELSE price
+    END as discounted_price
+FROM product;
+```
+
+In the next lesson, we'll explore date functions for working with temporal data.