This image shows the Orders table and the Order Items table joined on the Order ID column and the Orders table is set to Preserve Grain.

The Orders table data is:
Order ID Order Total
1001 50.97
1002 1249.91
The Order Items table data is:
Order ID Product ID Quantity
1001 40 1
1001 63 2
1002 29 1
1002 14 3
1002 2 1

This table shows the query output based on the Order table set to Preserve Grain. It shows that the Product ID column is NULL to preserve the grain at the Orders level.

Order ID Product ID Order Total Quantity
1001 NULL 50.97 3
1002 NULL 1249.91 5