How can I create “recursive sql”

问题

I want to make "link"

for Example, I have a 5 posts (id: "1", id: "2", id: "3", id: "4", id: "5")

and they have a sequence

{id:"1", nextId:"2"},
{id:"2", nextId:"4"} ,
{id:"3", nextId:"0"},
{id:"4", nextId:"3"},
{id:"5", nextId:"0"},

when I search from "1", I got a result : {id:"1"}, {id:"2"}, {id:"4"}, {id:"3"} when I search from "5", I got a result : {id:"5"}

How can I find All start with {id:"1"} in ANSI SQL?

select s.id, s.nextId from sample s
join sample ns on ns.id = s.nextId

It makes from first node to all.

I want to start "{some id}" and I want to use "limit 10"

help me!

回答1:

I don't have HSQLDB but something like this should do it:

WITH RECURSIVE chain(seq, me, next) AS (
  VALUES(0, CAST(null AS int), 1) -- start
  UNION ALL
  SELECT seq + 1, id, nextId
  FROM sample, chain
  WHERE id = next
)
SELECT * FROM chain WHERE seq > 0;

回答2:

create table links (id integer, nextid integer);

insert into links 
values 
(1, 2),
(2, 4),
(3, 0),
(4, 3),
(5, 0);

commit;

with recursive link_tree as (
   select id, nextid
   from links
   where id = 1  -- change this to change your starting node
   union all 
   select c.id, c.nextid
   from links c
     join link_tree p on p.nextid = c.id
)
select *
from link_tree;

This is ANSI SQL and works on HSQLDB, PostgreSQL, H2, Firebird, DB2, Microsoft SQL Server, Oracle 11.2 and several other engines - just not on MySQL (which does not support any of the modern SQL features which are state of the art nowadays).

回答3:

this works on sql server, maybe it will help you on HSQLDB

on your example, if you inform 1, it would return

2->4->3->0

its up to you if you want to add the 1 in the begining or maybe remove the 0 from the end

CREATE table test_sequence(
id int,
next_id int
)

insert into test_sequence VALUES(1,2)
insert into test_sequence VALUES(2,4)
insert into test_sequence VALUES(3,0)
insert into test_sequence VALUES(4,3)
insert into test_sequence VALUES(5,0)



alter function selectSequence(@id int)
returns varchar(max)
begin
    declare @next varchar(max)
    select @next=next_id from test_sequence WHERE id =@id
    if (@next != '') begin
        return @next +'->'+ dbo.selectSequence(@next)
    end else begin
        select @next=''
    end
    return @next
end

select dbo.selectSequence(1)

回答4:

The problem with recursion is clearly demonstrated by the other answers - the implementation is inconsistent across RDBMS vendors.

Alternatively, you can use the "nested set" model, which avoids recursion altogether, and should be easy to construct in a platform-agnostic SQL implementation.

来源：https://stackoverflow.com/questions/12950839/how-can-i-create-recursive-sql

标签

sql

recursion

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