Rename values in one column, depending on the value in other column

I have two tables with orders and parcels in MariaDB:

Orders

Parcels

and the following view:

CREATE OR REPLACE VIEW SHIPPING_LABELS AS SELECT
 DISTINCT(ORD.order_id) AS order_id,
 ORD.customer AS customer,
 ORD.payment AS payment
FROM orders ORD
 LEFT JOIN parcels PAR ON (ORD.order_id = PAR.order_id)
ORDER BY ORD.order_id DESC

This view generates the following result:

But, depending on the payment type, I need this result:

So, if there are more than 1 parcels and the payment is COD, it should be 1 row (DISTINCT). However, if the order is paid, the order_id should be renamed to _[1-...].

Is something like that possible in pure SQL?

Well, your current result is just select * from orders. It makes no sense to outer join a table, but not select anything from it and then use DISTINCT to remove the duplicate rows again created by the join.

What you want is to duplicate order rows in case the payment equals 'paid', so change the outer join accordingly. Then use window functions (COUNT OVER and ROW_NUMBER OVER) to decide whether to attatch numbers to the original order numbers and to get these numbers. Use a CASE expression to decide which kind of order number to display.

CREATE OR REPLACE VIEW shipping_labels AS
  SELECT
    CASE WHEN COUNT(*) OVER (PARTITION BY o.order_id) > 1 THEN
      CONCAT(p.order_id, '_', ROW_NUMBER() OVER (PARTITION BY p.order_id ORDER BY p.id))
    ELSE
      o.order_id
    END AS order_id,
    o.customer,
    o.payment
  FROM orders o
  LEFT JOIN parcels p ON p.order_id = o.order_id AND o.payment = 'paid';

Demo: https://dbfiddle.uk/tQNrSTC5