The Money Metrics: SUM and AVG

The Financial Question

The CFO walked in. *"What was our total revenue last quarter? And what was the average order value?"*

These are the two numbers that make or break a business presentation. Total Revenue tells شما the scale. Average Order Value (AOV) tells شما the customer quality.

The Quest: The Financial Functions

SQL has two more champion aggregation functions: `SUM()` and `AVG()`.

The Implementation: Calculating the Fortune

The Total

`SUM()` adds up all the values in a column.

-- Total revenue from all orders

SELECT SUM(order_amount) AS total_revenue

FROM orders;

The Average

`AVG()` calculates the mean of all the values.

-- Average order value

SELECT AVG(order_amount) AS avg_order_value

FROM orders;

All Together Now

You can (and should) put multiple aggregations in one query:

SELECT

COUNT(*) AS total_orders,

SUM(order_amount) AS total_revenue,

AVG(order_amount) AS avg_order_value

FROM orders;

The "Oops" Moment

I once ran `SUM()` on a column that contained NULLs in the middle of a migration. The sum was mysteriously lower than expected. Remember, `SUM()` ignores NULLs.

**Pro Tip**: If you suspect missing data, always run `COUNT(column)` alongside `SUM(column)` to see if the row counts match up.

The Victory

The CFO got a three-number summary that told the entire story of the quarter. I had turned a database of 100,000 transactions into a 3-second answer. That's the power of aggregation.

Your Task for Today

Run `SUM()` and `AVG()` on any numerical column. Put them in the same query and watch how SQL returns a single row of "Answers."

*Day 18: The Power of Grouping—GROUP BY.*