Why should you care?

Finance asks for total revenue today — SUM(Amount), not a loop in C# over every row.

See it live — copy this example

Run in SQL Server Management Studio (SSMS) or Azure Data Studio.

USE DataVerse;
SELECT
    COUNT(*) AS OrderCount,
    SUM(Amount) AS TotalRevenue,
    AVG(Amount) AS AvgOrder,
    MIN(Amount) AS Smallest,
    MAX(Amount) AS Largest
FROM dbo.Orders
WHERE City = N'Mumbai';

What happened?

• One result row describes Mumbai orders: how many, total money, average ticket, and extremes.
• WHERE limits which rows enter the aggregate.

Practice next

1. Run the query for Mumbai and for Pune.
2. Compare COUNT(*) vs COUNT(Amount) on a table with NULLs later.
3. Add SUM(Amount) FILTER style using CASE for Open cities only.
4. SUM(CASE WHEN Amount >= 1000 THEN Amount ELSE 0 END).
5. COUNT(DISTINCT City) across all orders.

Remember

Aggregates collapse many rows to metrics. WHERE restricts input rows. GROUP BY splits aggregates per key.

Daily GMV number

DataVerse ops board shows SUM(Amount) for today's orders.

Outcome: Leadership sees one trustworthy revenue figure.