Question

I need your help with this query I can’t solve.
Here’s the thing, let’s say I have a table like this:

Father | Son
1      |   2
1      |   3
1      |   4
3      |   5
3      |   6
2      |   7
4      |   8
5      |   9
6      |   10

So as you can see the table represents a father-son relationship, I need to find all the sons (and the sons of the sons) of one father, for example if Im looking for the sons of number 1 we will get a table like this

Father | son
1      |   2
1      |   3
1      |   4
1      |   5
1      |   6
1      |   7
1      |   8
1      |   9
1      |   10

If I’m lookeing for the sons of the number 3 we will get:

Father | son
3      |   5
3      |   6
3      |   9
3      |   10

okay I think you understood my point. The next problem is that I have to do it for each father in the table. So at the end, the table will be as follows:

Father | son
1      |   2
1      |   3
1      |   4
1      |   5
1      |   6
1      |   7
1      |   8
1      |   9
1      |   10
3      |   5
3      |   6
3      |   9
3      |   10
2      |   7
4      |   8
5      |   9
6      |   10

is pretty similar to go over a tree.
I have been trying to figure out this query for a while with not success. I did a code like this

WITH  son
        AS (
              -- in 
            SELECT  FK_CC_B
            FROM    PG_Rols_CC  
            WHERE   FK_CC_A = @idCC
            UNION ALL
              --recur
            SELECT  t.FK_CC_B
            FROM     PG_Rols_CC AS t
                    JOIN hijos AS a
                      ON t.FK_CC_A = a.FK_CC_B
           )
insert into @TableSons (idSon) SELECT * FROM son

But it doesn’t works for each father at the same time and the resulting table is a little bit different, it only has the son ID. Example

son
3
4
5
6
7

Hope you can help me.

Answer 1

If you want to get the descendents of all fathers, you need to get rid of the WHERE clause in the first part of your Common Table Expression (CTE).

If you want to output two columns (Father and Descendent), you need to add these columns to both parts of the CTE.

Like this:

WITH Son
AS
(
    SELECT
        FK_CC_A AS Father,
        FK_CC_B AS Son
    FROM
        PG_Rols_CC
    UNION ALL
    SELECT
        f.Father,
        s.FK_CC_B AS Son
    FROM
        Son f
        INNER JOIN PG_Rols_CC s ON f.Son = s.FK_CC_A
)

SELECT * FROM Son