CREATE OR REPLACE FUNCTION mix_table_fields(input_table_name VARCHAR, output_table_name VARCHAR, VARIADIC field_names VARCHAR[])
[...]

SELECT mix_table_fields('articles'::VARCHAR, 'output_random_articles'::VARCHAR, array['type'::varchar,'colour'::varchar,'size'::varchar,'price'::varchar]) ;

CREATE OR REPLACE FUNCTION public.mix_table_fields(
    IN input_table_name character varying,
    IN output_table_name character varying,
    VARIADIC field_names character varying[])