code: public static WindowOver<Double> regrSxx(Expression<? extends Number> arg1, Expression<? extends Number> arg2) {
          return new WindowOver<Double>(Double.class, SQLOps.REGR_SXX, arg1, arg2);
      }
docs: REGR_SXX makes the following computation after the elimination of null (arg1, arg2) pairs:
  
  <p>{@code REGR_COUNT(arg1, arg2) * VAR_POP(arg2)}</p>
  
  @param arg1 first arg
  @param arg2 second arg
  @return regr_sxx(arg1, arg2)