SQL Practice Problems - Day 8
Focus: Time-Series Window Functions

1 - Show each sale with the previous sale amount for the same product.
Input Table: Sales_Transactions
Output: Sale_ID, SKU_Code, Gross_Amount, Previous_Amount

2 - Calculate 3-day moving average of sales amounts.
Input Table: Sales_Transactions
Output: Date, Daily_Sales, Moving_Avg_3day

3 - Find the next sale date for each customer.
Input Tables: Customers, Sales_Transactions
Output: Customer_ID, Current_Sale_Date, Next_Sale_Date

4 - Compute cumulative sales by product category over time.
Input Tables: Products, Sales_Transactions
Output: Category, Date, Daily_Sales, Running_Total

5 - Identify sales with amounts that increased by more than 50% from previous sale.
Input Table: Sales_Transactions
Output: Sale_ID, Current_Amount, Previous_Amount, Pct_Increase

6 - Calculate running inventory changes from warehouse operations.
Input Tables: Warehouse_Ops
Output: Operation_ID, SKU_Code, Quantity, Running_Inventory

7 - Show monthly sales with difference from previous month.
Input Table: Sales_Transactions
Output: Month, Monthly_Sales, Previous_Month_Sales, Sales_Difference

8 - Find products with consistent weekly sales patterns.
Input Tables: Products, Sales_Transactions
Output: SKU_Code, Weekly_Sales_Variance

9 - Compute 7-day rolling sum of sales quantities.
Input Table: Sales_Transactions
Output: Date, Daily_Quantity, Rolling_Sum_7day

10 - Identify the longest gap between purchases for each customer.
Input Tables: Customers, Sales_Transactions
Output: Customer_ID, Max_Days_Between_Purchases

11 - Calculate the average time between purchases for each product.
Input Tables: Products, Sales_Transactions
Output: SKU_Code, Avg_Days_Between_Sales

12 - Show sales with the percentage change from the previous day's total sales.
Input Table: Sales_Transactions
Output: Date, Daily_Sales, Pct_Change_From_Previous_Day

13 - Find products with increasing sales for 3 consecutive months.
Input Tables: Products, Sales_Transactions
Output: SKU_Code, Month1_Sales, Month2_Sales, Month3_Sales

14 - Compute the exponential moving average (α=0.3) of daily sales.
Input Table: Sales_Transactions
Output: Date, Daily_Sales, EMA_03

15 - Identify the best selling day of week for each product category.
Input Tables: Products, Sales_Transactions
Output: Category, Best_Day, Avg_Sales_On_Best_Day