Grouping with GROUP BY

GROUP BY splits your data into groups and calculates aggregates for each group separately.

Syntax

SELECT column, AGGREGATE(other_column)
FROM table
GROUP BY column;

How It Works

Without GROUP BY, aggregates calculate across ALL rows. With GROUP BY, aggregates calculate for each unique value in the grouped column.

Exercises

Rule: Select Only Grouped or Aggregated Columns

When using GROUP BY, your SELECT can only include:

1. Columns in the GROUP BY clause
2. Aggregate functions

This is invalid:

-- ERROR: name is not grouped or aggregated
SELECT city, name, COUNT(*) FROM users GROUP BY city;

Free Practice

Try:

• Price statistics (min, max, avg) per category
• User count by city, sorted alphabetically
• Total inventory value per category