Looks like you're trying to create an SQL IN list. Here's another approach:
dt = New Table( "Untitled 81", Add Rows( 2 ),
New Column( "Column 1", Character, "Nominal", Set Values( {"Item1", "Item2"} ) ),
New Column( "Column 2", Character, "Nominal", Set Values( {"Value1", "Value2"} ) )
);
col1_list = column(dt, "Column 1") << get values;
col2_list = column(dt, "Column 2") << get values;
strcolumn1 = "('" || concat items(col1_list, "','") || "')";
strcolumn2 = "('" || concat items(col2_list, "','") || "')";
If any of the columns are numeric then the list returned from get values will be a matrix, and you will need to loop over the matrix to convert all elements to strings.