code: private Expression clip(ParserString raw) throws SQLParserException {
  	Expression exp = column(raw);
  	// if(exp==null)exp=brackedColumn(raw);
  	if (exp == null) exp = date(raw);
  	if (exp == null) exp = bracked(raw);
  	if (exp == null) exp = number(raw);
  	if (exp == null) exp = string(raw);
  	return exp;
      }
docs: STDDEV_POP | STDDEV_SAMP} ([ALL | DISTINCT][1]] Expression) } [[AS] label]