SQLite：如何查看不是我朋友但与我朋友是朋友的人

Question

我在 DB Browser 中有一个数据库，其中有两个表；

CREATE TABLE "User" (
    "ID"    integer NOT NULL,
    "name"  TEXT NOT NULL,
    PRIMARY KEY("ID" AUTOINCREMENT)
);

CREATE TABLE "Friends" (
    "UserID"    INTEGER NOT NULL,
    "FriendID"  INTEGER NOT NULL,
    FOREIGN KEY("UserID") REFERENCES "Anvandare"("ID") ON DELETE CASCADE
);

所以我的问题是，如何进行查询以显示我不是朋友但我的朋友是他们的朋友的人。这样我基本上就可以找到新朋友了。

Answer 1

您可以多次加入：

select distinct u.id, u.name
from friends f1                                   -- my friends
inner join friends f2 on f2.userid = f1.friendid  -- the friends of my friends
inner join users u on u.id = f2.friendid
where 
    f1.userid = ?
    and f2.friendid <> f1.userid
    and not exists (                               -- that are not my friends
        select 1 from friends f3 where f3.userid = ? and f3.friendid = f2.frienid
    )

SQLite：如何查看不是我朋友但与我朋友是朋友的人

SQLite: How to see people that aren't my friend, but are friends with my friends

sql

sqlite

inner-join

where-clause