gistfile1.sql

SET @broker=3, @product=1, @buy_status=3, @free=0;
SELECT price FROM (
    (
        SELECT t1.price FROM underrighting_product_tariffs as t1
    	LEFT JOIN ( SELECT COUNT(id) AS purchase_count FROM main_purchase
    			    WHERE status = @buy_status AND broker = @broker 
    				                           AND product = @product)
                    AS purchase 
    				ON purchase.purchase_count >= t1.`from` AND purchase.purchase_count <= t1.`to`
    	WHERE t1.product=1 
    	AND purchase.purchase_count IS NOT NULL
    	AND NOT EXISTS (SELECT t2.price FROM underrighting_product_broker_price as t2 
    					WHERE t2.broker=@broker AND t2.product=@product)
	)
    UNION
    (
        SELECT t2.price FROM underrighting_product_broker_price as t2 
		WHERE t2.broker=@broker AND t2.product=@product 
		                        AND t2.price IS NOT NULL
	)
) AS global WHERE price != @free