code: public static <D> SimpleExpression<D> as(Expression<D> source, Path<D> alias) {
          if (source == null) {
              return as(Expressions.<D>nullExpression(), alias);
          } else {
              return operation(alias.getType(), Ops.ALIAS, source, alias);
          }
      }
docs: Create a {@code source as alias} expression
  
  @param source source
  @param alias alias
  @param <D>
  @return source as alias