Aggregates turn raw data into business intelligence. They allow you to answer high-level questions without manually processing thousands of rows.
1Counting with Precision
Use COUNT(column_name) to count only rows where that column is NOT NULL. Use COUNT(*) to count every single row regardless of content. Knowing this difference is crucial for accurate reporting.
2The Power of SUM and AVG
These are the workhorses of financial applications. Whether calculating total revenue or average transaction size, these functions run natively in the database, making them much faster than calculating in your application code.
3Extremes: MIN and MAX
Finding the newest user (MAX(created_at)) or the oldest order (MIN(order_date)) is instantaneous with these functions. They work on dates and strings just as well as numbers.
