code: private Object executeExp(PageContext pc, SQL sql, Query qr, ZExp exp, int row) throws PageException {
  	if (exp instanceof ZConstant) return executeConstant(sql, qr, (ZConstant) exp, row);
  	else if (exp instanceof ZExpression) return executeExpression(pc, sql, qr, (ZExpression) exp, row);
  	throw new DatabaseException("unsupported sql statement [" + exp + "]", null, sql, null);
  
      }
docs: Executes a ZEXp
  
  @param sql
  @param qr Query Result
  @param exp expression to execute
  @param row current row of resultset
  @return result
  @throws PageException