sql - SQL：显示孩子和兄弟/姐妹

Question

我有一个数据库，基本上存储由几个家庭组成的家谱。

我有两张桌子：

1. "persons": id, name, lname
2. “关系”：父母，孩子

显示所有父母都可以，我这样做了：

SELECT DISTINCT p.fname, p.lname
FROM persons p
INNER JOIN relationships ON p.id = relationships.p
INNER JOIN persons c ON c.id = relationships.c;

但是我怎样才能全面地展示每个孩子及其各自的兄弟姐妹呢？

我在很多事情中尝试了一个选择，但它不起作用：

SELECT DISTINCT 
    c1.name, 
    c1.lname,
    (
    SELECT 
        c2.firstname, 
        c2.lastname 
    FROM 
        persons p2 
    INNER JOIN relations  ON p2.id = relations.parent 
    INNER JOIN persons c2 ON c2.id = relations.child
    WHERE 
        p.id = p2.id
    ) 
FROM 
    persons p
INNER JOIN relations  ON p.id  = relations.parent 
INNER JOIN persons c1 ON c1.id = relations.child;

我想我走错了路。

谢谢你的帮助。

Answer 1

如果我理解正确，这只是一个自我加入：

select r.child, r2.child as sibling
from relationships r join
     relationships r2
     on r.parent = r2.parent and
        r.child <> r2.child
order by r.child, r2.child;

对于其他表中的名称，您需要更多连接：

select p.*, p2.*
from relationships r join
     relationships r2
     on r.parent = r2.parent and
        r.child <> r2.child join
     persons p
     on p.id = r.child join
     persons p2
     on p2.id = r2.child
order by r.child, r2.child;