SQL Server中父级和子级关系的递归CTE

Question

Ok so I've seen a lot of examples online of this but I can't get it to work with my table.

Table: product
Columns: parent_product_id, child_product_id

If parent_product_id = child_product_id then the parent_product_id does not have a parent.

A child_product_id could be the parent of another record.

I tried to do this but it's taking forever for me to see the hierarchy of parent_product_id = 392193

;with  parents
        as ( 
            select  child_product_id,
                    parent_product_id
            from    product
            where   parent_product_id = child_product_id
            union all 
            select  e.child_product_id,
                    e.parent_product_id
            from    product e
            inner join parents m
            on      e.parent_product_id = m.child_product_id)
  select  *
  from    parents  
  where parents.parent_product_id = 392193
  option (maxrecursion 0)

Can anyone give me a hand?

Answer 1

You could move the start condition inside the CTE:

; with  parents as
        ( 
        select  child_product_id
        ,       parent_product_id
        from    product
        where   child_product_id = 392193
                and parent_product_id = 392193
        union all 
        select  e.child_product_id
        ,       e.parent_product_id
        from    parents m
        join    product e
        on      e.parent_product_id = m.child_product_id
        )
select  *
from    parents  
option  (maxrecursion 0)

An index on (parent_product_id, child_product_id) would help.

Usually, a child record refers to the primary key of its parent record. In your case, there's something unusual going on, with the parent having a "child_product_id". Some more information on this construct would clarify your question.

Answer 2

try this:

;with  parents
        as ( 
            select  parent_product_id,
                    child_product_id      
            from    product
            where   parent_product_id = child_product_id
            union all 
            select  m.parent_product_id, --this should be parent of top level
                    e.child_product_id   
            from    product e
            inner join parents m
            on      e.parent_product_id = m.child_product_id WHERE e.parent_product_id != e.child_product_id
            )
  select  *
  from    parents  
  where parents.parent_product_id = 392193
  option (maxrecursion 0)