[GENERAL] how to "group" several records with same timestamp into one line?

[zxo102 ouyang]

 Hi everyone,
     My data with same timestamp "2008-11-12 12:12:12" in postgresql are as
follows

rowid  data   unit            channel          create_on
------------------------------------------------------------------------------
 1        1.5     MPa          channel1  2008-11-12 12:12:12
 2        2.5     M3           channel2   2008-11-12 12:12:12
  3        3.5     M3           channel3   2008-11-12 12:12:12
  4        4.5     t               channel4   2008-11-12 12:12:12
------------------------------------------------------------------------------

I would like to "group" them into one line with SQL like

   1.5     MPa   2.5    M3  3.5  M3   4.5   t   2008-11-12 12:12:12


The table is defined as

CREATE TABLE record_data
(
  rowid serial NOT NULL,
  data double precision,
  unit character(10),
   channel character(20),
  create_on timestamp
)

Is that possible?   Thanks for your help in advance.

Ouyang