Concat result into one string

Question

I have following table
col1 col2
A mouse
B mouse
C mouse
D keyboard
E keyboard
I need to write a query which will give me an output
mouse - A, B, C

Answer 1

this?
SQL> WITH T AS
  2     (SELECT 'A' col1, 'mouse' col2  FROM DUAL
  3      UNION ALL
  4      SELECT 'B', 'mouse' VALUE FROM DUAL
  5      UNION ALL
  6      SELECT 'C' ,'mouse' VALUE FROM DUAL
  7      UNION ALL
  8      SELECT 'D' ,'keyboard' VALUE FROM DUAL
  9      UNION ALL
10     SELECT 'E', 'keyboard' VALUE FROM DUAL
11     )--------- end of data
12  SELECT col2
13        , SUBSTR(MAX(SYS_CONNECT_BY_PATH(col1, ',' )),2) con
14     FROM ( SELECT col2
15                 , col1
16                 , row_number() OVER (PARTITION BY col2 ORDER BY col2) rn
17              FROM T
18          )
19    START WITH rn = 1
20  CONNECT BY PRIOR rn = rn-1
21      AND PRIOR col2 = col2
22    GROUP BY col2;
COL2     CON
keyboard D,E
mouse    A,B,C