MERGE INTO customer_purchases AS targetUSING customer_purchases AS sourceON target.customer_id = source.customer_idWHEN MATCHED AND target.purchase_date < source.purchase_date THEN DELETE;

MERGE INTO customer_purchases AS targetUSING ( SELECT customer_id, purchase_date FROM customer_purchases WHERE purchase_date = (SELECT MAX(purchase_date) FROM customer_purchases GROUP BY customer_id)) AS sourceON target.customer_id = source.customer_idWHEN MATCHED THEN UPDATE SET target.* = source.*WHEN NOT MATCHED THEN INSERT *;

MERGE INTO customer_purchases AS targetUSING ( SELECT customer_id, MAX(purchase_date) AS latest_purchase_date FROM customer_purchases GROUP BY customer_id) AS sourceON target.customer_id = source.customer_idWHEN MATCHED AND target.purchase_date < source.latest_purchase_date THEN DELETEWHEN NOT MATCHED THEN INSERT *;

MERGE INTO customer_purchases AS targetUSING ( SELECT customer_id, MAX(purchase_date) AS latest_purchase_date FROM customer_purchases GROUP BY customer_id) AS sourceON target.customer_id = source.customer_id AND target.purchase_date < source.latest_purchase_dateWHEN MATCHED THEN DELETE;