@Override
  public String toString() {
    StringBuilder sb = new StringBuilder();

    for (Map.Entry<String, Map<String, ColumnInfo>> e : rslvMap.entrySet()) {
      String tab = e.getKey();
      sb.append(tab + "{");
      Map<String, ColumnInfo> f_map = e.getValue();
      if (f_map != null) {
        for (Map.Entry<String, ColumnInfo> entry : f_map.entrySet()) {
          sb.append("(" + entry.getKey() + "," + entry.getValue().toString()
              + ")");
        }
      }
      sb.append("} ");
    }
    return sb.toString();
  }
Get alias of the last table containing  column columnName

@param columnName column
@return table alias or null
ql/src/java/org/apache/hadoop/hive/ql/parse/RowResolver.java