Schematic description of the spectroscopic sample selection pipeline. The flowchart shows where a photometric target selection would be inserted in the spectroscopic selection pipeline. The photometric classifier performance is quantified by its precision and recall (defined in Sect. 2.1), while the final spectroscopic sample is characterised by the redshift purity and sample completeness. In this work, we use mock catalogues for the Euclid Wide and Deep surveys (see Sect. 3).