Is there any function in oracle similar like group_concat of mysql?

Answer

CREATE OR REPLACE FUNCTION get_comma_separated_value (input_val  in  number)
  RETURN VARCHAR2
IS
  return_text  VARCHAR2(10000) := NULL;
BEGIN
  FOR x IN (SELECT col2 FROM table_name WHERE col1 = input_val) LOOP
    return_text := return_text || ',' || x.col2 ;
  END LOOP;
  RETURN LTRIM(return_text, ',');
END;
/

So, you can do like:

select col1, get_comma_separated_value(col1) from table_name

Fiddle here

If you have got oracle 11g, you can use listagg :

SELECT
    col1,
    LISTAGG(col2, ', ') WITHIN GROUP (ORDER BY col2) "names"
FROM table_x
GROUP BY col1

Fiddle here for Listagg

For mysql, its gonna be simple:

SELECT col1, GROUP_CONCAT(col2) FROM table_name GROUP BY col1