[postgis-users] no union allowed in update?

[Biddy]

Hi everyone,

I am trying to do the following in plpgsql:

UPDATE lidarmpts set latlongalt =  
ST_Union(ST_GeomFromEWKT('SRID=4326;MULTIPOINT(' || lidarline.latitude  
|| ' ' || lidarline.longitude || ' ' || lidarline.elevation || ')' ))  
WHERE lidarline.rawlidarpts_id = counter;

The error I get is like:

ERROR:  cannot use aggregate function in UPDATE
LINE 1: UPDATE lidarmpts set latlongalt = ST_Union(ST_GeomFromEWKT('...
                                           ^
QUERY:  UPDATE lidarmpts set latlongalt =  
ST_Union(ST_GeomFromEWKT('SRID=4326;MULTIPOINT(' ||  $1  || ' ' ||  $2  
  || ' ' ||  $3  || ')' )) WHERE  $4  =  $5
CONTEXT:  PL/pgSQL function "fill_multipoint" line 10 at SQL statement

Now, the thing is that I had this snipped of code from before when I  
did stuff in Java and it was working perfectly fine.
However, now in plpgsql it has decided that I cannot do unions anymore  
in an update.

What's behind this?
How can I still update my multipoint?

All help is greatly appreciated,
cheers,
B.