Aggregates & groups

See the bigger picture

Lesson 7 of 20 · 7 min · Module 3: See patterns in data

Aggregate functions turn many rows into a useful summary. Count records, sum values, or calculate an average.

Start this lesson →

Free. No installation: you write and run the code in your browser, and it is checked automatically.

By the end, you’ll be able to…

Group rows sharing a value
Count records within a group
Distinguish an aggregate from a raw field

The idea

COUNT(*) counts rows. SUM(xp) adds values. Use GROUP BY to calculate a separate result for each group.

SELECT language, SUM(xp)
FROM learners
GROUP BY language;

01Group by the question’s category

GROUP BY language combines learners with the same profile language. COUNT(*) then produces one count for each group, so the result has one row per language.

02Choose coherent result columns

Select the grouping key and an aggregate value. Selecting another ungrouped, non-aggregated column can give a misleading or database-specific result.

Your turn

Select language and COUNT(*) for each language in the learners table. Group by language.

What the checks look for

Counts two JavaScript, two Python, and one SQL learner

Try it in the editor →

Take this with you

Grouping changes what one result row represents.