-- Database schema
| Country : CountryCode [ TEXT ] primary_key , ShortName [ TEXT ] , TableName [ TEXT ] , LongName [ TEXT ] , Alpha2Code [ TEXT ] , CurrencyUnit [ TEXT ] , SpecialNotes [ TEXT ] , Region [ TEXT ] , IncomeGroup [ TEXT ] , Wb2Code [ TEXT ] , NationalAccountsBaseYear [ TEXT ] , NationalAccountsReferenceYear [ TEXT ] , SnaPriceValuation [ TEXT ] , LendingCategory [ TEXT ] , OtherGroups [ TEXT ] , SystemOfNationalAccounts [ TEXT ] , AlternativeConversionFactor [ TEXT ] , PppSurveyYear [ TEXT ] , BalanceOfPaymentsManualInUse [ TEXT ] , ExternalDebtReportingStatus [ TEXT ] , SystemOfTrade [ TEXT ] , GovernmentAccountingConcept [ TEXT ] , ImfDataDisseminationStandard [ TEXT ] , LatestPopulationCensus [ TEXT ] , LatestHouseholdSurvey [ TEXT ] , SourceOfMostRecentIncomeAndExpenditureData [ TEXT ] , VitalRegistrationComplete [ TEXT ] , LatestAgriculturalCensus [ TEXT ] , LatestIndustrialData [ INTEGER ] , LatestTradeData [ INTEGER ] , LatestWaterWithdrawalData [ INTEGER ] | Series : SeriesCode [ TEXT ] primary_key , Topic [ TEXT ] , IndicatorName [ TEXT ] , ShortDefinition [ TEXT ] , LongDefinition [ TEXT ] , UnitOfMeasure [ TEXT ] , Periodicity [ TEXT ] , BasePeriod [ TEXT ] , OtherNotes [ INTEGER ] , AggregationMethod [ TEXT ] , LimitationsAndExceptions [ TEXT ] , NotesFromOriginalSource [ TEXT ] , GeneralComments [ TEXT ] , Source [ TEXT ] , StatisticalConceptAndMethodology [ TEXT ] , DevelopmentRelevance [ TEXT ] , RelatedSourceLinks [ TEXT ] , OtherWebLinks [ INTEGER ] , RelatedIndicators [ INTEGER ] , LicenseType [ TEXT ] | CountryNotes : Countrycode [ TEXT ] CountryNotes.Countrycode = Country.CountryCode , Seriescode [ TEXT ] CountryNotes.Seriescode = Series.SeriesCode , Description [ TEXT ] | Footnotes : Countrycode [ TEXT ] Footnotes.Countrycode = Country.CountryCode , Seriescode [ TEXT ] Footnotes.Seriescode = Series.SeriesCode , Year [ TEXT ] , Description [ TEXT ] | Indicators : CountryName [ TEXT ] , CountryCode [ TEXT ] Indicators.CountryCode = Country.CountryCode , IndicatorName [ TEXT ] , IndicatorCode [ TEXT ] , Year [ INTEGER ] , Value [ INTEGER ] | SeriesNotes : Seriescode [ TEXT ] SeriesNotes.Seriescode = Series.SeriesCode , Year [ TEXT ] , Description [ TEXT ] |
-- -- Mention the series code of countries using Australian dollar as their currency unit. Which country belongs to middle income group among them.

SELECT T1.CountryCode, T2.SeriesCode FROM Country AS T1 INNER JOIN CountryNotes AS T2 ON T1.CountryCode = T2.Countrycode WHERE T1.CurrencyUnit = 'Australian dollar' AND T1.IncomeGroup = 'Lower middle income';