OECD: mixed frequencies in series of FDI_AGGR_SUMM
See:
- one particular series in UI: https://db.nomics.world/OECD/FDI_AGGR_SUMM/ARG.SUB.DI.T_FA_F
- one particular series in API: https://api.db.nomics.world/v21/series?provider_code=OECD&dataset_code=FDI_AGGR_SUMM&series_code=ARG.SUB.DI.T_FA_F&format=json&orientation=row
- many series of this dataset in API: https://api.db.nomics.world/v21/series?provider_code=OECD&dataset_code=FDI_AGGR_SUMM&format=json
We can find years and years quarters in the same series.
Source: https://stats.oecd.org/viewhtml.aspx?datasetcode=FDI_AGGR_SUMM&lang=en