Write a SQL query to identify the number of policyholders who made a policy change, such as a coverage upgrade or downgrade, within 30 days of their initial purchase at Next insurance. Use the policy purchase and policy change records provided. Count each policyholder once, even if they changed multiple policies or made multiple changes.
Output
- Return one row with one column,
policyholder_count.
- Include changes occurring from the purchase date through exactly 30 days afterward.
- Return only the count of distinct policyholders.
