sql to create value dependent on prior record

This can be done in Firebird:

execute block returns(id_out integer,wo varchar(6),parent integer)
as
declare variable n integer;
declare variable i integer;
declare variable wo_old varchar(6);
begin
select count(*) from table1 into :n;
select id,name,id as parent from table1 order by id rows 1 to 1 into :id_out,:wo,arent;
suspend;
i=2;
while(i<=n) do begin
select name from table1 order by id rows i-1) to i-1) into :wo_old;
select id, name from table1 order by id rows :i to :i into :id_out, :wo;
if (wo_old=wo) then
parent=id_out-1;
else
parent=id_out;
i=i+1;
suspend;
end
end

It's a dynamic procedure, where name is your wo column. Tested & Works! Hope that help!
rtmpxr