docs: protected void processFromItem(FromItem fromItem, int level) {
          if (fromItem instanceof SubJoin) {
              SubJoin subJoin = (SubJoin) fromItem;
              if (subJoin.getJoinList() != null && subJoin.getJoinList().size() > 0) {
                  for (Join join : subJoin.getJoinList()) {
                      if (join.getRightItem() != null) {
                          processFromItem(join.getRightItem(), level + 1);
                      }
                  }
              }
              if (subJoin.getLeft() != null) {
                  processFromItem(subJoin.getLeft(), level + 1);
              }
          } else if (fromItem instanceof SubSelect) {
              SubSelect subSelect = (SubSelect) fromItem;
              if (subSelect.getSelectBody() != null) {
                  processSelectBody(subSelect.getSelectBody(), level + 1);
              }
          } else if (fromItem instanceof ValuesList) {
  
          } else if (fromItem instanceof LateralSubSelect) {
              LateralSubSelect lateralSubSelect = (LateralSubSelect) fromItem;
              if (lateralSubSelect.getSubSelect() != null) {
                  SubSelect subSelect = lateralSubSelect.getSubSelect();
                  if (subSelect.getSelectBody() != null) {
                      processSelectBody(subSelect.getSelectBody(), level + 1);
                  }
              }
          }
          //Table时不用处理
      }