// insert new condition as first element in a new vfilter (nvfilter), copy the content of vfilter and rename nvfilter back to vfilter.
HsqlArrayList nvfilter = new HsqlArrayList();
nvfilter.add(tf);
nvfilter.addAll(vfilter);
vfilter = nvfilter;
// set isOuterJoin correct
((TableFilter) vfilter.get(1)).isOuterJoin = true;