public Map<String, ColumnInfo> getFieldMap(String tabAlias) {
    if (tabAlias == null) {
      return rslvMap.get(null);
    } else {
      return rslvMap.get(tabAlias.toLowerCase());
    }
  }
Get a list of aliases for non-hidden columns
@param max the maximum number of columns to return
@return a list of non-hidden column names no greater in size than max
ql/src/java/org/apache/hadoop/hive/ql/parse/RowResolver.java