5.24Child relationship names with custom objects

Imagine:

Account
    ↓
Order__c

Maybe the parent-to-child relationship name is:

Orders__r

A custom relationship commonly uses:

__r

when traversing the relationship.

So you might encounter:

SELECT
    Id,
    Name,
    (
        SELECT Id, Order_Number__c
        FROM Orders__r
    )
FROM Account

Don't memorize the precise relationship name.

Look it up from Salesforce metadata/schema.

But recognize:

__c = custom field/object
__r = custom relationship traversal

That's useful.