mysql - 在mysql中选择不同的记录

Question

我的桌子

ANONYMOUS
ONE   TWO
1      2
2      1
1      2
3      1

现在我想选择一个和两个不同的集合。我选择的列表应该是

ANONYMOUS
    ONE   TWO
    1      2
    3      1

Answer 1

你的问题不是很清楚，但我想你的意思是：

SELECT DISTINCT one, two
FROM yourtable AS T1
WHERE one <= two
OR NOT EXISTS
(
     SELECT *
     FROM yourtable AS T2
     WHERE T1.one = T2.two
     AND T1.two = T2.one
)

它查找不存在(one, two)反向对的行。(two, one)如果两者都存在，它会选择这样的对one < two。它还选择值相等的行。

在线查看它：sqlfiddle

如果您更愿意使用 aJOIN而不是NOT EXISTS您可以这样做：

SELECT DISTINCT T1.one, T1.two
FROM yourtable AS T1
LEFT JOIN yourtable AS T2
ON T1.one = T2.two
AND T1.two = T2.one
WHERE T1.one <= T1.two
OR T2.one IS NULL

在线查看它：sqlfiddle

Answer 2

SELECT DISTINCT a.*
FROM        `ANONYMOUS` a
LEFT JOIN   `ANONYMOUS` b ON (a.one=b.two and a.two=b.one)
WHERE       b.one is null or a.one<b.one
ORDER BY    1,2