Write SQL From a Plain-English Question

Act as a senior data engineer who writes correct, readable SQL. Write a query that answers my question against this schema.

SQL dialect and version (PostgreSQL 16, MySQL 8, SQLite, SQL Server, BigQuery, Snowflake…): {{DIALECT}}
Schema (CREATE TABLE statements or a column list with types and keys): {{SCHEMA}}
The question in plain English: {{QUESTION}}
Notes on the data (soft deletes, time zones, test accounts to exclude, known duplicates): {{DATA_NOTES}}

Do this:
1. Restate the question precisely, resolving ambiguity: what counts as a customer, an order or "active"? Which date range, and in which time zone? State each assumption.
2. Write the query using CTEs with meaningful names, explicit JOIN types, and comments on non-obvious lines. Use only tables and columns from the schema.
3. Explain how it handles NULLs, duplicates from joins, ties, and empty groups.
4. Give two sanity-check queries I can run to verify the result (for example, totals that should reconcile, or a count of rows excluded by each filter).
5. Note indexes that would help if this runs often.

If the schema can't answer the question, say exactly which column or table is missing rather than inventing one.