问如果MYSQL插入中的语句不起作用

EN

    SET @key = (SELECT customer.key_stamp FROM customer WHERE customer.key_stamp = "0000");
    CASE WHEN (@key > 0) THEN 
        INSERT INTO transaction
                                (transaction.to, transaction.key, transaction.type, transaction.cost_bitcoin, transaction.quantity)
                                VALUES ("0000", "f5rwsd", 2, 0.0075, 
                                        (500000 + 
                                            (
                                                (SELECT bonus.amount
                                                    FROM bonus
                                                    WHERE 500000 BETWEEN bonus.min_quantity AND bonus.max_quantity
                                                ) / 500000
                                            ) * 100))
    END;