Sql 从结果中消除重复组合

我有这样一个选择结果：

from_loc    | to_loc   |
-------------------------
 A          |  B
------------------------
 B          |  C
------------------------
 B          |  A
------------------------  

如何从表中消除重复项，这意味着出现A到B，B到A意味着重复

我试图创造这样的结果，在尝试了几种方法后，我无法解决这个问题

from_loc    | to_loc   |
-------------------------
 A          |  B
------------------------
 B          |  C
------------------------

---

有谁能给我一些提示或参考，我怎样才能达到这样的结果？

试试

DISTINCT

然后

不存在
，比如：

SELECT DISTINCT from_loc, to_loc
FROM TableName A
WHERE NOT EXISTS
(
  SELECT from_loc, to_loc
  FROM TableName B
  WHERE A.from_loc = B.to_loc
  AND A.to_loc = B.from_loc
 )

DISTINCT
将从\u-loc-->从\u-loc
和
到\u-loc-->到\u-loc
虽然
不存在
将消除从\u loc-->到\u loc

的重复

，以及从\u loc

到\u loc-->的重复

但我没有测试此解决方案，但它可以有更好的性能（逻辑读取更少）：

DECLARE@MyTable表
(
from_loc VARCHAR（100）不为空，
to_loc VARCHAR（100）不为空
);
插入@MyTable（从_loc到_loc）值（'A'，'B'）；
插入@MyTable（从_loc到_loc）值（'B'，'C'）；
插入@MyTable（从_loc到_loc）值（'B'，'A'）；
选择不同的src.from_loc_new，src.to_loc_new
从…起
(
当x.从_loc选择案例时，可能在
行编号中使用此

案例：

WITH CTE AS( 
  SELECT from_loc, to_loc, 
         rn = row_Number() Over (Partition By  CASE WHEN from_loc > to_loc
                                    Then to_loc + '|' + from_loc 
                                    Else from_loc + '|' + to_loc END
                                 Order By from_loc, to_loc)
  FROM dbo.TableName
)
SELECT from_loc, to_loc FROM cte WHERE rn = 1

---

假设您的原始SQL是：

SELECT from_loc, to_loc FROM route;

将其用作与

左连接

连接在一起的子查询两次。然后，使用

IF

清楚地选择所需字段

SELECT DISTINCT
  IF (y.from_loc IS NULL, x.from_loc,
    IF(x.from_loc < x.to_loc, x.from_loc, x.to_loc)) AS from_loc,
  IF (y.from_loc IS NULL, x.to_loc,
    IF(x.from_loc > x.to_loc, x.from_loc, x.to_loc)) AS to_loc
FROM (
) AS x
  SELECT from_loc, to_loc FROM route
LEFT JOIN (
  SELECT from_loc, to_loc FROM route
) AS y
ON x.from_loc = y.to_loc AND x.to_loc = y.from_loc;

在MySQL客户端应用程序上尝试以下操作：

SELECT DISTINCT
  IF (y.from_loc IS NULL, x.from_loc,
    IF(x.from_loc < x.to_loc, x.from_loc, x.to_loc)) AS from_loc,
  IF (y.from_loc IS NULL, x.to_loc,
    IF(x.from_loc > x.to_loc, x.from_loc, x.to_loc)) AS to_loc
FROM (
) AS x
  SELECT "A" AS from_loc, "B" AS to_loc
  UNION SELECT "B", "C"
  UNION SELECT "B", "A"
LEFT JOIN (
  SELECT "A" AS from_loc, "B" AS to_loc
  UNION SELECT "B", "C"
  UNION SELECT "B", "A"
) AS y
ON x.from_loc = y.to_loc AND x.to_loc = y.from_loc;

选择DISTINCT
如果（y.from_loc为空，x.from_loc，
如果（x.from_locx.到位置，x.从位置，x.到位置））关于位置
从(
)AS x
从位置选择“A”，从位置选择“B”
联合选择“B”、“C”
联合选择“B”、“A”
左连接(
从位置选择“A”，从位置选择“B”
联合选择“B”、“C”
联合选择“B”、“A”
)如同
在x上，从_loc=y.到_loc，x.到_loc=y.从_loc；

---

我知道这不是一个有效的解决方案，但它很有效！

发布您当前的SQL查询Hi Shai，我的查询非常大，为了让它更容易理解，我在这里放了一个非常简化的场景。谢谢！这将消除重复的两个副本，即删除

A | B

和

B | A

。这个问题需要一个保留这两行如果只有一个值为（'D'，'C'）的记录会发生什么？这个SQL会将其反转为（'C'，'D'），对吗？这就是您想要的吗？@OchiWansa:2&3）是的。

SELECT "A" AS from_loc, "B" AS to_loc
UNION SELECT "B", "C"
UNION SELECT "B", "A";

SELECT DISTINCT
  IF (y.from_loc IS NULL, x.from_loc,
    IF(x.from_loc < x.to_loc, x.from_loc, x.to_loc)) AS from_loc,
  IF (y.from_loc IS NULL, x.to_loc,
    IF(x.from_loc > x.to_loc, x.from_loc, x.to_loc)) AS to_loc
FROM (
) AS x
  SELECT "A" AS from_loc, "B" AS to_loc
  UNION SELECT "B", "C"
  UNION SELECT "B", "A"
LEFT JOIN (
  SELECT "A" AS from_loc, "B" AS to_loc
  UNION SELECT "B", "C"
  UNION SELECT "B", "A"
) AS y
ON x.from_loc = y.to_loc AND x.to_loc = y.from_loc;