SELECT * 
FROM `fao-maps.fao_zonal_stats_views.vw_MODIS_006_MOD16A2_FAO_GAUL_2015_level2_ET`
where (country in UNNEST(SPLIT(@country,",")) or "All" in UNNEST(SPLIT(@country,",") )) AND
    date >= @start_date AND
      date <= @end_date