UNION or JOIN for SELECT from multiple tables

Question

My Issue

I am trying to select one row from multiple tables based on parameters, but my limited knowledge of SQL joining is holding me back. Could somebody possibly point me in the right direction?

Consider these table structures:

+-----------------------+     +---------------------+
| Customers             |     | Sellers             |
+-------------+---------+     +-----------+---------+
| Customer_ID | Warning |     | Seller_ID | Warning |
+-------------+---------+     +-----------+---------+
| 00001       | Test 1  |     | 00008     | Testing |
| 00002       | Test 2  |     | 00010     | Testing |
+-------------+---------+     +-----------+---------+

What I would like to do is one SELECT to retrieve only one row, and in this row will be the 'Warning' field for each of the tables based on the X_ID field.

Desired Results

So, if I submitted the following information, I would receive the following results:

Example 1:

Customer_ID = 00001
Seller_ID = 00008

Results:
+-----------------------------------+
| Customer_Warning | Seller_Warning |
+------------------+----------------+
| Test 1           | Testing        |
+------------------+----------------+

Example 2:

Customer_ID = 00001
Seller_ID = 00200

Results:
+-----------------------------------+
| Customer_Warning | Seller_Warning |
+------------------+----------------+
| Test 1           | NULL           |
+------------------+----------------+

What I Have Tried

This is my current code (I am receiving loads of rows):

SELECT c.Warning 'Customer_Warning', s.Warning AS 'Seller_Warning'
FROM Customers c,Sellers s
WHERE c.Customer_ID = @Customer_ID
    OR s.Seller_ID = @Seller_ID

But I have also played around with UNION, UNION ALL and JOIN. Which method should I go for?

Answer 1

Since you're not really joining tables together, just selecting a single row from each, you could do this:

SELECT 
    (SELECT Warning 
     FROM Customers 
     WHERE Customer_ID = @Customer_ID) AS Customer_Warning,
    (SELECT Warning 
     FROM Sellers 
     WHERE Seller_ID = @Seller_ID) AS Seller_Warning