Exclude free subscribers via anti-join

You work with a subscriptions fact table and a small months calendar. A "new subscriber" is defined as a company on the month of its first paid subscription (based on the earliest start_date in Subscriptions for that company). Using the tables below, write a query that: 1) Computes monthly new-subscriber counts. 2) Zero-fills months using Month_Calendar so that every month in the calendar appears, even if there were no new subscribers. 3) Adds year-over-year (YoY) metrics by comparing each month to the same calendar month in the previous year. 4) Excludes any company that ever appears in Free_Subs from *all* months and *all* derived YoY metrics. The anti-join must occur **before** calculating first-subscription dates and monthly aggregations, so that excluded companies do not affect zero-filled months or YoY baselines. 5) Is resilient to duplicate company_id values in Free_Subs (i.e., your anti-join logic must not break if duplicates are present). The final output must have exactly these columns and types: - month_start (DATE) – first day of the month from Month_Calendar - year (INT) - month (INT) – numeric month (1–12) - new_subscribers (INT) – count of companies whose first paid subscription falls in that calendar month, **excluding** companies in Free_Subs - prev_year_new_subscribers (INT) – new_subscribers for the same month in the previous year (0 if that prior month is not present or had no new subscribers) - yoy_abs_change (INT) – new_subscribers - prev_year_new_subscribers - yoy_pct_change (DECIMAL(10,2)) – (new_subscribers - prev_year_new_subscribers) / prev_year_new_subscribers * 100; return NULL when prev_year_new_subscribers = 0 to avoid division by zero. Additionally, in SQL comments within your query, briefly explain the trade-offs between using NOT EXISTS versus LEFT JOIN ... IS NULL for this anti-join under typical OLAP columnar engines (e.g., Snowflake, BigQuery, Redshift).