Question

I am building a navigation menu from a list of pages.
The table is like this:

Table name: pages

id | type | parent | name
-------------------------------
1,    1,     null,   root1
2,    1,     null,   root2
3,    2,     2,      home
4,    2,     3,      child
5,    2,     4,      sub_child
6,    3,     5,      sub_sub_child


type:
1 = root page / site
2 = page
3 = ...

My problem is that from any page, I have to find the root page.
I have a column parent that refers to the parent page, except for the root pages.

I can have multiple root pages in the table, but each page has only one parent.

Could somebody help me to write a recursive query ?

I’m trying to use this query, but it doesn’t work:

with recursive pages (id, parent) as 
(
    select pages.id, 
    pages.parent, 
    from pages
    where pages.id = 4

union all
    select pages.id, 
    pages.parent,
    from pages
    inner join pages p on p.id = pages.parent
)
select id
from pages;

Thanks

Answer 1

My farovite trick to handle tree structured data in database is add a column FullID to table to avoid complex (parhaps recursive) SQLs/Stored Procedures.

FullID     id  parent   name
-----------------------------
1          1   null     root1
2          2   null     root2
2.3        3   2        home
2.3.4      4   3        child
2.3.4.5    5   4        sub_child
2.3.4.5.6  6   5        sub_sub_child

So, to find the root page id, just extract the first part of FullID via SQL or your application language.

If using SQL, you can use the following SQL to get the root id.

-- MySQL dialect
select substring_index(FullID,'.',1) as RootID from table;

-- SQL Server dialect
select case charindex('.', FullID) when 0 then FullID else substring(FullID, 1, charindex('.', FullID)-1) end as RootID from table

To delete a node and it’s children

DELETE table WHERE id=<CURRENT_NODE_ID> OR FullID LIKE '<CURREN_NODE_FULLID>.%'

To move a node and it’s children

-- change the parent of current node:
UPDATE table
SET parent=<NEW_PARENT_ID>
WHERE id=<CURRENT_NODE_ID>

-- update it's FullID and all children's FullID:
UPDATE table
SET FullID=REPLACE(FullID,<CURRENT_NODE_PARENT_FULLID>, <NEW_PARENT_FULLID>)
WHERE (id=<CURRENT_NODE_ID> OR FullID LIKE '<CURRENT_NODE_FULLID>.%')

Note

This trick is only applied on limited tree level cases, or the FullID can’t hold long content if tree level is too deep.