@Override
 public void visit(CompareCriteria obj) {
   preVisitVisitor(obj);
   visitNode(obj.getLeftExpression());
   visitNode(obj.getRightExpression());
   postVisitVisitor(obj);
 }
 private Expression rewriteMultiSourceCommand(Command command) throws TeiidComponentException {
   Expression result = null;
   if (command instanceof StoredProcedure) {
     StoredProcedure obj = (StoredProcedure) command;
     for (Iterator<SPParameter> params = obj.getMapOfParameters().values().iterator();
         params.hasNext(); ) {
       SPParameter param = params.next();
       if (param.getParameterType() != SPParameter.IN) {
         continue;
       }
       if (metadata.isMultiSourceElement(param.getMetadataID())) {
         Expression source = param.getExpression();
         params.remove();
         if (param.isUsingDefault()
             && source instanceof Constant
             && ((Constant) source).isNull()) {
           continue;
         }
         result = source;
         break;
       }
     }
   }
   if (command instanceof Insert) {
     Insert obj = (Insert) command;
     for (int i = 0; i < obj.getVariables().size(); i++) {
       ElementSymbol elem = obj.getVariables().get(i);
       Object metadataID = elem.getMetadataID();
       if (metadata.isMultiSourceElement(metadataID)) {
         Expression source = (Expression) obj.getValues().get(i);
         obj.getVariables().remove(i);
         obj.getValues().remove(i);
         result = source;
         break;
       }
     }
   } else if (command instanceof FilteredCommand) {
     for (Criteria c : Criteria.separateCriteriaByAnd(((FilteredCommand) command).getCriteria())) {
       if (!(c instanceof CompareCriteria)) {
         continue;
       }
       CompareCriteria cc = (CompareCriteria) c;
       if (cc.getLeftExpression() instanceof ElementSymbol) {
         ElementSymbol es = (ElementSymbol) cc.getLeftExpression();
         if (metadata.isMultiSourceElement(es.getMetadataID())
             && EvaluatableVisitor.willBecomeConstant(cc.getRightExpression())) {
           if (result != null && !result.equals(cc.getRightExpression())) {
             return Constant.NULL_CONSTANT;
           }
           result = cc.getRightExpression();
         }
       }
     }
   }
   return result;
 }