Lesson 14 — CASE inside aggregates (pivot)

CASE inside aggregates: a pivot table

Put CASE inside SUM or COUNT to count only certain rows per group. This turns rows into columns — a pivot. SUM(CASE WHEN status = 'paid' THEN amount ELSE 0 END) adds only paid amounts.

SELECT month,
  SUM(CASE WHEN status = 'paid' THEN amount ELSE 0 END) AS paid
FROM invoices GROUP BY month

Why it matters: "paid vs unpaid per month" side by side in one row is exactly what managers want in a spreadsheet.