Mail Merge Word and Excel that filters multiple rows for each merge

Hi,

I think it's because it's the end of the day that the right words are escaping me, so I'm reaching out here cause Google is getting me nowhere.

So say a company sends out invoices to clients. And each invoice has various charges and dates that the clients owes on. So it's not like a basic, flat mail merge where its Dear [NameHere], Please come to my party.. It's more like Dear [NameHere], Here's a list of what you owe followed by one or many rows of data such as charges and dates and balances and such that are attached to that one merge.

And that's the part that's confusing me. At this late hour in my workday I can conceptualize a flat-file of merge data, but that's not what I need. I need a merge that can dig into each client to include the rows of data related to the client, and include all those rows on the merge. Can you point me in the right direction?

Thanks.