Table columns are selectable using the selection range property of a table. The following information is from the range section of this website.

Column Reference

To target a whole single column, use the value of the column name or index properties to address the range of cells contained by the column.

tell thisTable
 set the selection range to column "H"
end tell

Multiple Columns

To target a multiple contiguous columns, use the opposing corners technique, referencing the two corner cells by their relative position in their columns.

tell thisTable
 set thisRangeName to ¬
 ((name of the first cell of column "C") & ":" & ¬
 (name of the last cell of column "E"))
 set the selection range to range thisRangeName
end tell

You can also create a range for a contiguous group of full columns by using their names, like this:

tell thisTable
 set thisRangeName to "C:E"
 set the selection range to range thisRangeName
end tell