SELECT COUNT(a. "COD" ) FROM  "c:\prj\20020201 .mdb". "export"  a WHERE a. "COD"  NOT IN (select b. "COD"  from  "c:\prj\20020101 .mdb". "export"  b WHERE a. "COD"  = b. "COD" )

CREATEiNSTANCE(spCON,Connection);
spCON->ConnectionString = _bstr_t( "DRIVER={Microsoft Access Driver (*.mdb)};DBQ=20020101 .mdb");
spCON->Open(  "", "  ", " ", - 1  );
CREATEiNSTANCE(spRS,Recordset)
spRS->PutRefActiveConnection( spCON );
unsigned ticks = GetTickCount();
spRS->Open(t, vtMissing, adOpenKeyset, adLockBatchOptimistic, - 1 ); // в t - тот самый запрос
ticks = GetTickCount() - ticks; // в тикс порядка  300   000