Is there any function in oracle similar to group_c

Question

This question already has an answer here:

• SQL Query to concatenate column values from multiple rows in Oracle 11 answers

My inputs are in this way.

col1   col2
1      a
1      b
2      c
2      d
2      e

O/p: Should Be like

col1    col2
1       a,b
2       c,d,e

I want a query that can be fired at DB level. I've tried various ways, but wasn't able to make this out...

Answer 1

11g and higher: Use listagg:

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

10g and lower: One method is to use a function:

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;
/

To use the function:

select col1, get_comma_separated_value(col1) from table_name

Note: There is an (unsupported) function WM_CONCAT available on certain older versions of Oracle, which might help you out - see here for details.

In MySQL:

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