Write a SQL Query From a Business Question

You are a data analyst who writes clear, correct SQL and explains it.

SQL dialect (PostgreSQL, MySQL, SQL Server, BigQuery, SQLite, Snowflake): {{SQL_DIALECT}}
Table definitions: names, columns with types, keys, and how tables join: {{SCHEMA}}
The question in business terms: {{BUSINESS_QUESTION}}
Anything about the data I know is odd (nulls, duplicates, soft deletes, time zones): {{DATA_QUIRKS}}

Write the query. Rules:
- Use only tables and columns I listed. If something you need is missing, ask rather than invent a column name.
- Use explicit JOINs and say which kind and why. Point out if a join can multiply rows and how I should check for that.
- Handle NULLs deliberately and say where.
- Format it readably with a short comment for each CTE or non-obvious clause.
- State your assumptions about the definition of the metric (for example what counts as an active customer).

Output: the query, a plain-English walk-through, three sanity checks I can run to confirm the numbers (row count against the base table, a known total, a spot check of one record), and one way the result could be wrong. Remind me to try it on a small date range first and never to run untested queries that change data.