JoinSelect 为什么只支持两张表的连表呢？

[bigbaibaibai]

public class SqlParser {
  // ...
  public JoinSelect parseJoinSelect(SQLQueryExpr sqlExpr) throws SqlParseException {
      MySqlSelectQueryBlock query = (MySqlSelectQueryBlock) sqlExpr.getSubQuery().getQuery();

      List<From> joinedFrom = findJoinedFrom(query.getFrom());
      if (joinedFrom.size() != 2)
          throw new RuntimeException("currently supports only 2 tables join");

      JoinSelect joinSelect = createBasicJoinSelectAccordingToTableSource((SQLJoinTableSource) query.getFrom());
      List<Hint> hints = parseHints(query.getHints());
      joinSelect.setHints(hints);
      String firstTableAlias = joinedFrom.get(0).getAlias();
      String secondTableAlias = joinedFrom.get(1).getAlias();
      Map<String, Where> aliasToWhere = splitAndFindWhere(query.getWhere(), firstTableAlias, secondTableAlias);
      Map<String, List<SQLSelectOrderByItem>> aliasToOrderBy = splitAndFindOrder(query.getOrderBy(), firstTableAlias, secondTableAlias);
      List<Condition> connectedConditions = getConditionsFlatten(joinSelect.getConnectedWhere());
      joinSelect.setConnectedConditions(connectedConditions);
      fillTableSelectedJoin(joinSelect.getFirstTable(), query, joinedFrom.get(0), aliasToWhere.get(firstTableAlias), aliasToOrderBy.get(firstTableAlias), connectedConditions);
      fillTableSelectedJoin(joinSelect.getSecondTable(), query, joinedFrom.get(1), aliasToWhere.get(secondTableAlias), aliasToOrderBy.get(secondTableAlias), connectedConditions);

      updateJoinLimit(query.getLimit(), joinSelect);

      //todo: throw error feature not supported:  no group bys on joins ?
      return joinSelect;
  }
 // ...
}

这里看出来写死了只支持 2个表的join，为什么不将所有连表以数组或list的方式存储起来呢