Count, sum, group
How many active accounts, what revenue per plan, what share of a given status: these monthly-review questions all rely on aggregation. The lesson shows how to summarize a table and compare groups in SQL, and how to avoid the most common counting mistakes. You then present numbers the data team can sign off on without redoing them.
Lesson objective
By the end of this lesson, you will be able to summarize a table with aggregate functions (COUNT, SUM, AVG, MIN, MAX), compute these summaries per group with GROUP BY, filter groups with HAVING and count a subset of rows with CASE WHEN or COUNT(DISTINCT).
Topics covered
- GROUP BY
- COUNT DISTINCT
- HAVING
- aggregate functions
- product metrics
In the glossary
Where it fits
First queries
How do I get a reliable number from a table myself, without being caught out by missing values and dates?
Lessons in this module
- Load the dataset and write your first SELECT queries
- Count, sum, group (this lesson)
- Missing values and dates, two traps that produce wrong numbers
What you will learn in this module
This lesson is part of the course Model your product’s data and query it with SQL
- Write queries that filter, sort and aggregate (SELECT, WHERE, ORDER BY, GROUP BY, HAVING) while handling NULL values and dates correctly.
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