SQL -- 删除重复对
我正在使用 SQLite 来存储一组使用两列 u 和 v 的图的无向边.例如:
I'm using an SQLite to store a set of undirected edges of a graph using two columns, u and v. For example:
u v
1 2
3 2
2 1
3 4
我已经通过 SELECT DISTINCT * FROM 边完成了它并删除了所有重复的行.
I have already been through it with SELECT DISTINCT * FROM edges and removed all duplicate rows.
然而，如果我们还记得这些是无向边，仍然会有重复.在上面的例子中，边 (1,2) 出现了两次，一次是 (1,2)，一次是 (2,1)，它们都是等价的.
However, there are still duplicates if we remember these are undirected edges. In the above example, the edge (1,2) appears twice, once as (1,2) and once as (2,1) which are both equivalent.
我希望删除所有此类重复项，只留下其中一个，即 (1,2) 或 (2,1) - 哪个并不重要.
I wish to remove all such duplicates leaving only one of them, either (1,2) or (2,1) -- it doesn't really matter which.
任何想法如何实现这一目标?谢谢！
Any ideas how to achieve this? Thanks!
推荐答案
如果存在相同对(反向)，则取 u>v 所在的那个.
If the same pair (reversed) exists take the one where u>v.
SELECT DISTINCT u,v
FROM table t1
WHERE t1.u > t1.v
OR NOT EXISTS (
SELECT * FROM table t2
WHERE t2.u = t1.v AND t2.v = t1.u
)
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