String clause = assembleJoinClause(leftName, rightName, semantic);
JoinClause clause = createJoinClause(leftName, rightName, semantic);
    public void addJoinClause(String leftName,                              String rightName,                              int semantic) {        String clause = assembleJoinClause(leftName, rightName, semantic);        _alreadyJoined.insertObjectAtIndex(clause, 0);    }