SQL “tree-like” query - most parent group

Question

I\'m having some trouble doing a \"tree-like\" query (what do we call this?) in SQL.

Take a look at my diagram below (table and column names are in danish - sorry ab

Answer 1

You can use CTE's to construct "the full path" column on the fly

--DROP TABLE Gruppe, Kunde, Gruppe_Gruppe, Kunde_Gruppe
CREATE TABLE Gruppe (
    Id                  INT PRIMARY KEY
    , Name              VARCHAR(100)
    )
CREATE TABLE Kunde (
    Id                  INT PRIMARY KEY
    , Name              VARCHAR(100)
    )
CREATE TABLE Gruppe_Gruppe (
    ParentGruppeId      INT
    , ChildGruppeId     INT
    )
CREATE TABLE Kunde_Gruppe (
    KundeId             INT
    , GruppeId          INT
    )

INSERT      Gruppe
VALUES      (1, 'Group 1'), (2, 'Group 2'), (3, 'Group 3')
            , (4, 'Sub-group A'), (5, 'Sub-group B'), (6, 'Sub-group C'), (7, 'Sub-group D')

INSERT      Kunde
VALUES      (1, 'Kunde 1'), (2, 'Kunde 2'), (3, 'Kunde 3')

INSERT      Gruppe_Gruppe
VALUES      (1, 4), (1, 5), (1, 7)
            , (2, 6), (2, 7)
            , (6, 1)

INSERT      Kunde_Gruppe
VALUES      (1, 1), (1, 2)
            , (2, 3), (2, 4)

;WITH       CTE
AS          (
            SELECT      CONVERT(VARCHAR(1000), REPLACE(CONVERT(CHAR(5), k.Id), ' ', 'K')) AS TheKey
                        , k.Name        AS Name
            FROM        Kunde k

            UNION ALL

            SELECT      CONVERT(VARCHAR(1000), REPLACE(CONVERT(CHAR(5), x.KundeId), ' ', 'K')
                             + REPLACE(CONVERT(CHAR(5), g.Id), ' ', 'G')) AS TheKey
                        , g.Name
            FROM        Gruppe g
            JOIN        Kunde_Gruppe x
            ON          g.Id = x.GruppeId

            UNION ALL

            SELECT      CONVERT(VARCHAR(1000), p.TheKey + REPLACE(CONVERT(CHAR(5), g.Id), ' ', 'G')) AS TheKey
                        , g.Name
            FROM        Gruppe g
            JOIN        Gruppe_Gruppe x
            ON          g.Id = x.ChildGruppeId
            JOIN        CTE p
            ON          REPLACE(CONVERT(CHAR(5), x.ParentGruppeId), ' ', 'G') = RIGHT(p.TheKey, 5)
            WHERE       LEN(p.TheKey) < 32 * 5
            )
SELECT      *
            , LEN(TheKey) / 5 AS Level
FROM        CTE c
ORDER BY    c.TheKey

Performance might be sub-optimal if you have lots of reads vs rare modifications.