/* Создаем таблицы */
create table GRAPH_NODES
(
  NAME      VARCHAR(5)       not null
);
alter table GRAPH_NODES add constraint GRAPH_PK primary key (NAME);
create table GRAPH_EDGES
(
  NODE1     VARCHAR(5)       not null,
  NODE2     VARCHAR(5)       not null,
  WEIGHT    DECIMAL(10,0)    not null
);
alter table GRAPH_EDGES add constraint GRAPH_EDGES_NODE1_FK foreign key (NODE1) references GRAPH_NODES (NAME);
alter table GRAPH_EDGES add constraint GRAPH_EDGES_NODE2_FK foreign key (NODE2) references GRAPH_NODES (NAME);
alter table GRAPH_EDGES add constraint GRAPH_EDGES_CIRCLE check (node1 <> node2);
create table DEXTRA
(
  NODE      VARCHAR(5)       not null,
  WEIGHT    DECIMAL(18,0)    not null
);
alter table DEXTRA add constraint DEXTRA_PK primary key (NODE);
alter table DEXTRA add constraint DEXTRA_NODE_FK foreign key (NODE) references GRAPH_NODES (NAME);
/* Заполняем таблицы */
insert into GRAPH_NODES (NAME) values ('A');
insert into GRAPH_NODES (NAME) values ('B');
insert into GRAPH_NODES (NAME) values ('C');
insert into GRAPH_NODES (NAME) values ('D');
insert into GRAPH_NODES (NAME) values ('E');
insert into GRAPH_NODES (NAME) values ('F');
insert into GRAPH_EDGES (NODE1 , NODE2 , WEIGHT) values ('A' , 'B' , 1);
insert into GRAPH_EDGES (NODE1 , NODE2 , WEIGHT) values ('A' , 'C' , 5);
insert into GRAPH_EDGES (NODE1 , NODE2 , WEIGHT) values ('B' , 'C' , 2);
insert into GRAPH_EDGES (NODE1 , NODE2 , WEIGHT) values ('C' , 'D' , 7);
insert into GRAPH_EDGES (NODE1 , NODE2 , WEIGHT) values ('C' , 'E' , 9);
insert into GRAPH_EDGES (NODE1 , NODE2 , WEIGHT) values ('D' , 'E' , 3);
insert into GRAPH_EDGES (NODE1 , NODE2 , WEIGHT) values ('D' , 'F' , 5);
insert into GRAPH_EDGES (NODE1 , NODE2 , WEIGHT) values ('E' , 'F' , 5);
commit;
/* Подготоваливаем таблицу DEXTRA */
delete from DEXTRA;
insert into DEXTRA select NAME NODE, 9999999999 WEIGHT from GRAPH_NODES;
commit;
/* Подготоваливаем начальную точку */
update DEXTRA set WEIGHT = 0 where NODE = 'A';
/* Заполняем таблицу DEXTRA (я это делал процедурой) */
DECLARE VARIABLE RESULT INTEGER;
DECLARE VARIABLE NODE_NAME VARCHAR(5);
DECLARE VARIABLE NODE_WEIGHT DECIMAL(10,0);
begin
  RESULT = 1;
  while RESULT > 0 do
  begin
    RESULT = 0;
    for select T3.NODE2 NODE, (T3.WEIGHT + T2.WEIGHT) WEIGHT
        from DEXTRA T1, DEXTRA T2, GRAPH_EDGES T3
        where T1.NODE = T3.NODE2 and T2.NODE = T3.NODE1 and T1.WEIGHT > (T3.WEIGHT + T2.WEIGHT)
        into :NODE_NAME , :NODE_WEIGHT do
    begin
      update DEXTRA set WEIGHT = :NODE_WEIGHT where NODE = :NODE_NAME;
      RESULT = RESULT + 1;
    end
  end
end