SUM adds numeric values across rows and can be used after a JOIN to calculate totals for related entities.
Total sales, transaction values, salaries, balances, and expenses are common business metrics calculated using SUM.
Calculate total order value for every customer.
SELECT
c.CustomerName,
SUM(o.OrderAmount) AS TotalSales
FROM Customers c
LEFT JOIN Orders o
ON c.CustomerID = o.CustomerID
GROUP BY c.CustomerName;SUM with JOIN is widely used in sales, finance, banking, inventory, and management reporting.
- SUM calculates numeric totals.
- JOIN connects the amounts to business entities.
- GROUP BY defines the level of aggregation.
- NULL values are ignored by SUM.
- COALESCE can be used when a zero result is preferred.
How is SUM used with JOIN?
SUM can aggregate numeric values from a related table after joining it to another business entity.
What happens when SUM has no matching rows?
SUM can return NULL, so COALESCE may be used when the desired display value is zero.