title: Check if character field contains only digits
body: <p>I read data from a excel file.
  The cols of internal table all are char128, there are 2 cols contain only digital with decimal point. So I need to check the fields only contain digital or digital with decimal point.</p>
  
  <p>The function module NUMERIC_CHECK, just can check only digital, if the digital with decimal point it will be useless.</p>