COUNT with conditional CASE

Question

Accepted Answer

COUNT ignores NULLs. When CASE finds no matching WHEN and has no ELSE, it returns NULL - so non-matching rows contribute nothing to the count. Alice has 1 shipped order (the pending row produces NULL and is skipped by COUNT). Bob has 2 shipped orders. This is cleaner than a subquery: one pass over the table computes per-customer counts for any number of statuses simultaneously.