Ecommerce SQL Query Set

# Submission: Ecommerce SQL Query Set ## Brief Write 5 correct queries against the messy `orders` CSV (broken joins, duplicate keys, null customer ids): (1) top-2 orders per customer, (2) days-since-last-order with >30-day flags, (3) monthly running revenue, (4) longest active streak per user (gaps-islands), (5) CTE refactor of one nested query. ## Dataset `orders` CSV + train/holdout split. Train shows expected row counts; holdout is hidden and used for grading. Quarantine rules for null keys are part of the score. ## Starter guardrails (88) - Use the provided skeleton with 5 labeled query slots; one query per slot. - CTEs only for nesting deeper than 2 levels; explicit `ROWS` frames on all running aggregates; no `SELECT *` in final outputs. ## Deterministic checks All 5 queries execute without error; row counts match train; holdout exact-match on queries 1–3 within tolerance on 4–5. ## 100-pt rubric - Correctness per query (5 x 12 pts): 60 - CTE readability + explicit frames (15 pts) - Null-key quarantine handling (10 pts) - Deterministic holdout match (10 pts) - One-paragraph method note (5 pts)