PLPGSQL function that returns the number of rows of a given array of tables in a 'table_name', 'count' format

table_rows.md

CREATE OR REPLACE FUNCTION table_rows(tables text[])
RETURNS TABLE (table_name text, count bigint) AS $$
DECLARE
  query text := '';
BEGIN
  FOR i IN 1..array_length(tables, 1) LOOP
    query := query || format('SELECT %L as table_name, count(*) from %s', tables[i], tables[i]);
    IF i < array_length(tables, 1) THEN
      query := query || ' union all ';
    END IF;
  END LOOP;
  RETURN QUERY EXECUTE query;
END $$ LANGUAGE plpgsql;
-- Output
--
--     table_name     |  count   
----------------------+----------
-- public.tags        |    35100
-- public.diagnostics | 15833383
-- public.readings    | 15830114
-- (3 rows)
--