How to Query MAX SQLFunction by Query Builder?\

In order to query the latest WTpart 'version', etc  A,B.C...etc.

querySpec：

            QuerySpec qs1 = new QuerySpec();              qs1.setAdvancedQueryEnabled(true);             int classIndex = qs1.appendClassList( wt.part.WTPart.class, false );             SQLFunction fun=new SQLFunction(SQLFunction.MAXIMUM,new ClassAttribute( wt.part.WTPart.class , "versionInfo.identifier.versionId" ) );                qs1.appendSelect(fun, newint[] { classIndex }, false);             qs1.appendWhere(new SearchCondition( wt.part.WTPartMaster.class , "number" , "=" , "test_number" ),WTPartMasterIndex );    

The query result always throw exception

"A statement with aggregate function can not be used with access control."

I try to  change SQLFunction  MAXIMUM to "LENGTH", and It is work.

What's the hell? What can I do  resovle the query requirement?