begin atomic
  for xxx as 
    select c from  table( f('a') ) as T
  do
    insert into t2 ( p1 ) values (c);
  end for;
end

begin atomic
  for xxx as
    select c from  table( f('a') ) as T
  do
    insert into t2 ( p1 ) values (c);
  end for;
end
DB21034E  The command was processed as an SQL statement because it was not a
valid Command Line Processor command.  During SQL processing it returned:
SQL20267N  The function "VVM.F" (specific "SQL060622164835800") modifies SQL
data and is invoked in an illegal context. Reason code =  "2".  LINE NUMBER= 3 .
SQLSTATE=429BL

begin atomic
  for xxx as
    with temp as (select c from  table( f('a') ) as T)
    select * from temp
  do
    insert into t2 ( p1 ) values (c);
  end for;
end
DB21034E  The command was processed as an SQL statement because it was not a
valid Command Line Processor command.  During SQL processing it returned:
SQL0901N  The SQL statement failed because of a non-severe system error.
Subsequent SQL statements can be processed.  (Reason "column number out of
range".)  SQLSTATE= 58004 

begin atomic
  declare x varchar( 10 );
  for xxx as
    select c from  table( f('a') ) as T
  do
    set x = c;
  end for;
end
DB21034E  The command was processed as an SQL statement because it was not a
valid Command Line Processor command.  During SQL processing it returned:
SQL20267N  The function "VVM.F" (specific "SQL060622164835800") modifies SQL
data and is invoked in an illegal context. Reason code =  "2".  LINE NUMBER= 4 .
SQLSTATE=429BL