code: public static String getAllColumns(Class<?> entityClass) {
          Set<EntityColumn> columnSet = EntityHelper.getColumns(entityClass);
          StringBuilder sql = new StringBuilder();
          for (EntityColumn entityColumn : columnSet) {
              sql.append(entityColumn.getColumn()).append(",");
          }
          return sql.substring(0, sql.length() - 1);
      }
docs: 获取所有查询列，如id,name,code...
  
  @param entityClass
  @return