docs: public static String getSelectColumns(Class<?> entityClass) {
          EntityTable entityTable = getEntityTable(entityClass);
          if (entityTable.getBaseSelect() != null) {
              return entityTable.getBaseSelect();
          }
          Set<EntityColumn> columnList = getColumns(entityClass);
          StringBuilder selectBuilder = new StringBuilder();
          boolean skipAlias = Map.class.isAssignableFrom(entityClass);
          for (EntityColumn entityColumn : columnList) {
              selectBuilder.append(entityColumn.getColumn());
              if (!skipAlias && !entityColumn.getColumn().equalsIgnoreCase(entityColumn.getProperty())) {
                  //不等的时候分几种情况，例如`DESC`
                  if (entityColumn.getColumn().substring(1, entityColumn.getColumn().length() - 1).equalsIgnoreCase(entityColumn.getProperty())) {
                      selectBuilder.append(",");
                  } else {
                      selectBuilder.append(" AS ").append(entityColumn.getProperty()).append(",");
                  }
              } else {
                  selectBuilder.append(",");
              }
          }
          entityTable.setBaseSelect(selectBuilder.substring(0, selectBuilder.length() - 1));
          return entityTable.getBaseSelect();
      }