The columns of the child band apply to all child rows. So there's no way to hide a column under some parent rows and not under others.

I suppose if you coded your application to collapse all other rows when a row is expanded, and thus had only one row expanded at any time, then you could set the hidden property on the columns in the BeforeRowExpand event and thus achieve what you want.

Another option would be to set up your data structure with multiple child bands where each parent row only had child rows in one of those child bands. But depending on the number of possible combinations of hidden columns you want, this could be very inefficient.

Still another option would be to use an UltraTree instead of an UltraGrid. The tree allows you to assign a ColumnSet to a collection of nodes, so you could have different hidden columns in each collection, or even on each individual node. But the tree lacks certain grid features like summaries and filtering.