若要使用「分組方式」一次更新多個非重複行，請執行以下操作：

Question

我遵循Generate a random number of non duplicated random number in [0, 1001] through a loop的幫助。

但我不能適用於我的情況。當我這樣做：

update weighed_directed_edge set endpoint= trunc(1000 * random()+ 1) 
from generate_series(1,10) group by 1 where startpoint= from_point; 

更新的EndpointId它抱怨：

ERROR: syntax error at or near "group" 
LINE 1: ...nc(1000 * random()+ 1) from generate_series(1,10) group by 1. 

我也試過：

insert into weighed_directed_edge (startpoint,endpoint) 
values (from_point, trunc((1000 * random()+ 1)) 
FROM generate_series(1, directed2number) 
GROUP BY 1 ; 

insert into weighed_directed_edge (startpoint, endpoint, costs) 
select 1, trunc(1000 * random()+ 1) from generate_series(1,10) group by 1,1; 

不工作。我需要從另一個表中設置的相同點中選擇起點和終點，以填充weighed_directed_edge表。

• cross_point table：有1001個十字路口。

         Table "public.cross_point" 
      Column | Type |         Modifiers        
  --------------+---------+--------------------------------------------------------------------- 
  intersection | integer | not null default nextval ('intersection_intersection_seq'::regclass) 
  x_axis  | integer | not null 
  y_axis  | integer | not null 
  Indexes: 
      "intersection_pkey" PRIMARY KEY, btree (intersection) 
      "intersection_x_axis_key" UNIQUE, btree (x_axis, y_axis) 
  

• weighed_directed_edge表：

   Table "public.weighed_directed_edge" 
       Column |  Type  | Modifiers 
      ------------+------------------+----------- 
      startpoint | integer   | 
      endpoint | integer   | 
      costs  | double precision | 
      Indexes: 
       "weighed_directed_edge_startpoint_key" UNIQUE, btree (startpoint, endpoint) 
      Foreign-key constraints: 
       "weighed_directed_edge_endpoint_fkey" FOREIGN KEY (endpoint) REFERENCES cross_point(intersection) 
       "weighed_directed_edge_startpoint_fkey" FOREIGN KEY (startpoint) REFERENCES cross_point(intersection) 
  

• 的隨機數端點（從1001點列隨機得到）對應於每一個起始點（從柱依次點獲得）,. 終點的數量在[1,7]。

• 成本將基於起點和終點之間的距離。

要求：

• 起始點和終點的組合應該是唯一的。

• Startpoints集包含從表cross_point所有1001相交

• 端點來全部來自同一交叉點集。

• 每個星點最多有7個端點匹配，（7路道路交叉點最大），並且隨機選擇端點匹配數量。

我跳過下面的代碼成本計算：

--The largest number of intersection chosen is 7, but this could be altered 
create or replace function popluate_weighed_directed_edge() returns void as $$ 
declare 
from_point integer; 
to_point integer; 
directed2number integer; --the number of node this startpoint leads to 
counter integer; 
factor float; 
weight numeric; 
start_pointer record; 

begin 
for start_pointer in select * from cross_point 
loop 
from_point := start_pointer.intersection; 
    directed2number := trunc(Random()*7+1); 
    counter := directed2number; 
     while counter > 0 
     loop 
insert into weighed_directed_edge (startpoint) select from_point from generate_series(1,10) ; 
update weighed_directed_edge set endpoint= trunc(1000 * random()+ 1) from generate_series(1,10) group by 1 where startpoint= from_point ; 
update weighed_directed_edge set costs= trunc(1000 * random()+ 1) from generate_series(1,10) group by 1 where startpoint= from_point ; 
     counter := counter - 1; 
     end loop; 
end loop; 
end 
$$ language plpgsql; 

Answer 1

在循環中，你可以畫一個隨機數，僅將其插入（和遞減循環計數器），如果它不存在。 Pseudocode：

while (counter > 6) 
loop: 
    this = 1+ random() *1000 
    insert into weighed_directed_edge (startpoint, endpoint, costs) 
    VALUES (:frompoint, :this, xxx* random()) 
    WHERE NOT EXISTS (
    SELECT(*) FROM weighed_directed_edge nx 
    WHERE nx.startpoint = :frompoint 
    AND nx.endpoint = :this 
    ); 

    if (rowcount > 0) counter -= 1; 
end loop;