CASE Inside Aggregates for Buckets

Overview

CASE combined with COUNT and GROUP BY lets you build histogram-style buckets directly in SQL. Here we classify each employee into a salary band (under 70k, 70-90k, 90-110k, and 110k-plus) and count how many employees land in each band.

The Query

Step-by-Step Breakdown

1. CASE — maps each salary to a band label using ordered WHEN branches.
2. COUNT(*) — tallies employees per band.
3. GROUP BY salary_band — one row per distinct band label produced.

Variations

Bucket movies by decade:

Common Mistakes

• Overlapping WHEN clauses. Because CASE stops at the first match, an out-of-order range can silently misclassify rows.
• Non-grouped CASE column in SELECT. The exact CASE expression must appear in GROUP BY (or be aliased consistently).
• Missing ELSE. Rows matching no WHEN become NULL; group them intentionally if needed.