How do I great a top header that spans columns in a straight table?

[#1]

How do I great a top header that spans columns in a straight table?

[Gysbert_Wassenaar]

With text box objects placed over the headers of the straight table. There's no way to do this directly using only the straight table.

[rsdhavle]

i have added text boxes as suggested by many. But when i make different selections in the document the table size varies and hence text boxes gets misplaced. Any workaround on that?