Task

Write a correct SQL query to satisfy {Business Question} using {Dialect} (e.g., Postgres, BigQuery, Snowflake).

Context

Schema: {Tables and Columns}. Filters: {Filters}. Grain: {Desired Grain}. Edge cases: {Edge Cases}.

Requirements

• Produce the SQL with clear CTEs and comments.
• Explain joins, grain, and why aggregations are correct.
• Add 3 validation queries/tests (row counts, null checks, reconciliation).
• Optimize for readability first, then note performance improvements (indexes/partitioning).

Output Format

• SQL Query
• Explanation
• Validation Tests
• Performance Notes

Notes

If schema is incomplete, infer likely keys and clearly label assumptions. Warn about double-counting and fan-out joins.