Oracle SQL cara menulis pernyataan sql yang memverifikasi apakah pengguna di jaringan saya (yaitu teman atau teman dari teman)

SELECT  *
FROM    (
        SELECT  username
        FROM    friends
        START WITH
                username = 'myname'
        CONNECT BY
                friendname = PRIOR username
                AND level <= 3
        )
WHERE   username = 'friendname'
        AND rownum = 1

Perbarui level seperlunya:Anda dapat mencari teman lapis ketiga, dll.

Jika hubungan pertemanan simetris, Anda harus membuat kueri berikut:

WITH    q AS
        (
        SELECT  username, friendname
        FROM    friends
        UNION ALL
        SELECT  friendname, username
        FROM    friends
        ),
        f AS
        (
        SELECT  friendname, level
        FROM    q
        START WITH
                username = 'Thomas'
        CONNECT BY NOCYCLE
                username = PRIOR friendname
        )
SELECT  *
FROM    f
WHERE   friendname = 'Jo'
        AND rownum = 1

Kueri ini dapat dibuat lebih cepat jika Anda mendenormalisasi tabel Anda:simpan dua catatan per pertemanan, seperti ini:

CREATE TABLE dual_friends (orestes NOT NULL, pylades NOT NULL, CONSTRAINT pk_dualfriends_op PRIMARY KEY (orestes, pylades)) ORGANIZATION INDEX
AS
SELECT  username, friendname
FROM    friends
UNION ALL
SELECT  friendname, username
        FROM    friends

Kemudian Anda tinggal mengganti CTE di atas dengan dual_friends :

WITH    f AS
        (
        SELECT  pylades, level
        FROM    dual_friends
        START WITH
                orestes  = 'Thomas'
        CONNECT BY NOCYCLE
                orestes = PRIOR pylades
                AND level <= 3
        )
SELECT  *
FROM    f
WHERE   pylades = 'Jo'
        AND rownum = 1

, yang akan menggunakan indeks dan jauh lebih efisien, terutama jika Anda membatasi level ke nilai yang wajar.