Skip to content
SQLSimplified
group by

SUM() Aggregation With GROUP BY

Sum total units ordered per product category using SUM() grouped by category.

Overview

SUM() adds up a numeric column across rows. Paired with GROUP BY, it answers "total X per Y" questions, such as total units sold per product category in the store.

The Query

Loading playground environment...

Step-by-Step Breakdown

  1. SUM(o.quantity) totals units sold per category.
  2. SUM(o.quantity * p.price) computes revenue per category by multiplying before summing.
  3. GROUP BY p.category defines the buckets.

Aggregate then compute

SUM(quantity * price) multiplies inside each row, then sums, different from SUM(quantity) * SUM(price), which would be wrong.

Variations

Sum order quantities per customer city:

Loading playground environment...

Common Mistakes

  • SUM of a text column. SUM requires numbers; summing a name errors.
  • Mixing SUM with non-grouped columns. Every selected column must be grouped or aggregated.
  • Ignoring NULLs. SUM ignores NULL values, which is usually what you want, but be aware it won't treat them as zero.

Related examples

Core Aggregate Functions: COUNT, SUM, AVG, MIN, MAX
aggregate
A single query demonstrating all five core aggregates over the employees table.
GROUP BY Basics: Aggregating Rows Into Summaries
group by
Collapse individual orders into one summary row per customer using GROUP BY, COUNT, and SUM.
GROUP BY with HAVING
group by
Use HAVING to keep only departments whose average salary exceeds a threshold after aggregation.

Cite this resource

SQLSimplified. "SUM() Aggregation With GROUP BY Example". Available at: https://sqlsimplified.online/examples/group-by-sum