Is it possible for the script to select multiple columns of the current text box, or multiple columns of the entire table (excluding the header and footer)?

Prerequisite: I have already selected cells from multiple columns

Hi ​@dublove , This is another example of the problems you will run into when scripting selections. You have to test what the selection is, and there can be a lot of possible and unexpected variables—is it text, page item, image, table, cell, table inside of a cell, etc. etc.

You could try something like this, which works on your sample:

//this assumes selection[0] is [object Cell]
var s = app.activeDocument.selection[0]
var col = s.cells[0].parentColumn.cells

for (var i = 1; i < col.length; i++){
    try {
        if (col[i].insertionPoints[0].horizontalOffset == col[0].insertionPoints[0].horizontalOffset) {
           col[i].select(SelectionOptions.ADD_TO)
        } 
    }catch(e) {}    
};   

Result with your example:

But if I change the position of the text frames so they align vertically I get this: