public void addRHSSemijoinColumns(String alias, List<ASTNode> columns) {
    List<ASTNode> cols = rhsSemijoin.get(alias);
    if (cols == null) {
      rhsSemijoin.put(alias, columns);
    } else {
      cols.addAll(columns);
    }
  }
Remeber the mapping of table alias to set of columns.

@param alias
@param columns
ql/src/java/org/apache/hadoop/hive/ql/parse/QBJoinTree.java