如何使用 IF() 条件在 MySQL 中显示真假行

订单

+---------+------------+----------------+----------+------------+
| OrderID | CustomerID | DateOfPurchase | Discount | DueDate    |
+---------+------------+----------------+----------+------------+
|      82 |          7 | 2022-04-17     | 0        | 2022-05-17 |
|      83 |         91 | 2022-04-17     | 0        | 2022-05-17 |
|      84 |          8 | 2022-04-17     | 0        | 2022-05-17 |
|      85 |         91 | 2022-04-17     | 0        | 2022-05-17 |
|      86 |          7 | 2022-04-17     | 0        | 2022-05-17 |
|      87 |         91 | 2022-04-18     | 0        | 2022-05-18 |
|     109 |          7 | 2022-04-25     | 0        | 2022-05-25 |
+---------+------------+----------------+----------+------------+

客户表

+------------+----------+-------+-------+-------------+-----------------------------+----------+--------------+
| CustomerID | Fname    | Mname | Lname | Contact_no  | Address                     | Valid_id | Credit_Limit |
+------------+----------+-------+-------+-------------+-----------------------------+----------+--------------+
|          7 | John     | Dale  | Doe   | 09123654789 | Asan Sur, Sison, Pangasinan | NULL     |     5000.000 |
|          8 | Jane     | Dale  | Doe   | 09987654123 | Asan Sur, Sison, Pangasinan | NULL     |     1500.000 |
|         91 | Kurdapya | Buang | Selos | 09741258963 | Paldit, Sison, Pangasinan   | NULL     |     5000.000 |
+------------+----------+-------+-------+-------------+-----------------------------+----------+--------------+

付款表

+-----------+------------+---------+------------+----------+
| PaymentID | CustomerID | OrderID | PayDate    | Amount   |
+-----------+------------+---------+------------+----------+
|        20 |          7 |      82 | 2022-04-25 |  800.000 |
|        21 |         91 |      83 | 2022-04-17 | 2500.000 |
|        22 |         91 |      85 | 2022-04-17 |  200.000 |
|        23 |         95 |      88 | 2022-04-18 | 2122.000 |
|        24 |         96 |      90 | 2022-04-25 |  577.000 |
|        25 |         97 |     111 | 2022-04-25 |    0.000 |
|        26 |         98 |     114 | 2022-04-25 |  166.000 |
|        27 |         99 |     115 | 2022-04-25 | 1740.000 |
+-----------+------------+---------+------------+----------+

我想知道客户Kurdapya(OrderID=91)的订单ID中哪些是付费的，哪些是未付费的

这是我到目前为止try 过的问题

try 1:

select if(py.OrderID=r.OrderID, 'paid','unpaid') as remarks, r.OrderID, r.CustomerID
from orders r,
     payment py
where py.OrderID = r.OrderID and r.CustomerID = 91
GROUP by r.OrderID;

try 1的结果:

+---------+---------+------------+
| remarks | OrderID | CustomerID |
+---------+---------+------------+
| paid    |      83 |         91 |
| paid    |      85 |         91 |
+---------+---------+------------+

try 2:

select if(py.OrderID=r.OrderID and py.OrderID=py.Amount!='null', 'paid','unpaid') as remarks, r.OrderID, r.CustomerID
from orders r,
     payment py
where r.CustomerID = 91
GROUP by r.OrderID;

Result of try 2:

+---------+---------+------------+
| remarks | OrderID | CustomerID |
+---------+---------+------------+
| unpaid  |      83 |         91 |
| unpaid  |      85 |         91 |
| unpaid  |      87 |         91 |
+---------+---------+------------+

My DESIRED RESULT IS THIS:

    +---------+---------+------------+
    | remarks | OrderID | CustomerID |
    +---------+---------+------------+
    | unpaid  |      83 |         91 |
    | unpaid  |      85 |         91 |
    | paid    |      87 |         91 |
    +---------+---------+------------+