snowflake_lead_and_lag_functions

Snowflake supports window functions like `LEAD` and `LAG` for analyzing data within a specific window or partition. Here are some use cases demonstrating the usage of `LEAD` and `LAG` functions in Snowflake SQL queries:

1. Comparing Values in Sequential Rows
   
   Assume you have a table named `sales_data` with columns `sale_date` and `revenue`. You want to compare the revenue of the current row with the revenue of the next row using `LEAD` function.

   ```sql
   SELECT 
       sale_date,
       revenue,
       LEAD(revenue) OVER (ORDER BY sale_date) AS next_revenue
   FROM 
       sales_data
   ORDER BY 
       sale_date;
   ```

2. Calculating the Difference Between Current and Previous Values
   
   If you want to find the difference in revenue between the current row and the previous row using `LAG` function:

   ```sql
   SELECT 
       sale_date,
       revenue,
       LAG(revenue) OVER (ORDER BY sale_date) AS prev_revenue,
       revenue - LAG(revenue) OVER (ORDER BY sale_date) AS revenue_difference
   FROM 
       sales_data
   ORDER BY 
       sale_date;
   ```

3. Handling Partitions - Calculate Difference per Group

   For partitioned data, say you want to find the difference in revenue between the current row and the previous row within each product category:

   ```sql
   SELECT 
       product_category,
       sale_date,
       revenue,
       LAG(revenue) OVER (PARTITION BY product_category ORDER BY sale_date) AS prev_revenue,
       revenue - LAG(revenue) OVER (PARTITION BY product_category ORDER BY sale_date) AS revenue_difference
   FROM 
       sales_data
   ORDER BY 
       product_category, sale_date;
   ```

4. Predicting Future Values

   Suppose you want to forecast sales revenue by comparing the current revenue with the future revenue using `LEAD` function:

   ```sql
   SELECT 
       sale_date,
       revenue,
       LEAD(revenue, 1, 0) OVER (ORDER BY sale_date) AS future_revenue_1_month
   FROM 
       sales_data
   ORDER BY 
       sale_date;
   ```

5. Using Default Values with LEAD or LAG

   You can specify default values for the `LEAD` or `LAG` functions, especially helpful for handling NULLs:

   ```sql
   SELECT 
       sale_date,
       revenue,
       LEAD(revenue, 1, 0) OVER (ORDER BY sale_date) AS next_revenue_with_default
   FROM 
       sales_data
   ORDER BY 
       sale_date;
   ```