Here's one way to do it:
dt = New Table( "Test Zeroes", Add Rows( 3 ),
New Column( "Column 1", Character, "Nominal", Set Values( {"a", "b", "c"} ) ),
New Column( "Column 2", Numeric, "Continuous", Format( "Best", 12 ),
Set Values( [1, ., 3] ) ),
New Column( "Column 3", Numeric, "Continuous", Format( "Best", 12 ),
Set Values( [., 2, .] ) )
);
col_list = dt << get column names(string, numeric);
For( i = 1, i <= N Items( col_list ), i++,
missing_rows = dt << get rows where (is missing(as column(dt, col_list[i])));
if (nrows(missing_rows) > 0,
column(dt, col_list[i])[missing_rows] = 0;
);
);