Sharepoint List - Parent/Child relationship in single list?

asapboston Are you trying to add lookup column from same SharePoint list (as lookup parent list & child list)? If yes, it is possible in SharePoint to create lookup column based on same list.

Check this documentation: Create list relationships by using lookup columns 

Also check my responses on this thread: SharePoint list self join? 

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asapboston SharePoint lists are not a full relational database, but you can achieve what you want by grouping list items. In this example we've got the names of people attending a course. Initially it's just the All Items view.

From the dropdown in the top right of the list a new view called Group By Course has been created. Then edit the view again from the dropdown in the top right. In the screen that appears scroll down to the Group By section and group by the appropriate column which in this case is Title as it holds the name of the course. Set the group to be collapsed or expanded by default. I've also set the Totals to be displayed.

Select the view and the courses will be grouped with the numbe rof people attending each course. Clicking on the > will expand the group.

Rob
Los Gallardos
Intranet, SharePoint and Power Platform Manager (and classic 1967 Morris Traveller driver)