optional UNION ALL: CLI option '--on-duplicate-relation' with values 'fail' and 'insert' (later more modes)
examples, shortcuts:
relpipe-tr-unionall() { relpipe-tr-sql --copy '.+' --on-duplicate-relation insert; } # does UNION ALL for all tables with same name (including already existing ones – when non-empty database is used)
relpipe-tr-unionall() { relpipe-tr-serialize | relpipe-tr-deserialize; } # does UNION ALL only for tables with same name immediately following each other (interleaved duplicates will stay unaffected)