UPDATE table SET col = (SELECT ...)

Hello,

If I understand the SQL references I have read, UPDATEs are allowed to
pull data from SELECT statements, something like

  UPDATE table SET col1 = (SELECT val1 FROM table WHERE id = 34),
               SET col2 = (SELECT val2 FROM table WHERE id = 34)
         WHERE id = 35;

However, the PostgreSQL parser chokes on the 'SELECT'. The
documentation says

  UPDATE table SET column = expression [, ...]
      [ FROM fromlist ]
      [ WHERE condition ]

  expression = A valid expression or value to assign to column.


I don't know exactly how to interpret `valid expression'.

--
Eric Marsden
emarsden @ mail.dotcom.fr
It's elephants all the way down