Sql 删除包含可能包含相同数据的两列的行

以以下数据为例

Letter One | Letter Two    
         A | B
         B | A
         A | C

如何只选择具有相同数据的任何行，因此在本例中，我希望输出删除第二行，因为这两个字母是相同的。 所以我的输出是：

Letter One | Letter Two
         A | B 
         A | C

---

假设没有精确的副本，您可以执行以下操作：

select letterA, letterB
from t
where letterA <= letterB
union all
select letterA, letterB
from t
where letterA > letterB and
      not exists (select 1 from t t2 where t2.letterA = t.letterB and t2.letterB = t.letterA);

select distinct (case when letterA <= letterB then letterA else letterB end) as letterA,
       (case when letterA > letterB then letterA else letterB end) as letterB
from t;

如果不关心最后一列的顺序，可以执行以下操作：

select letterA, letterB
from t
where letterA <= letterB
union all
select letterA, letterB
from t
where letterA > letterB and
      not exists (select 1 from t t2 where t2.letterA = t.letterB and t2.letterB = t.letterA);

select distinct (case when letterA <= letterB then letterA else letterB end) as letterA,
       (case when letterA > letterB then letterA else letterB end) as letterB
from t;

---

假设没有精确的副本，您可以执行以下操作：

select letterA, letterB
from t
where letterA <= letterB
union all
select letterA, letterB
from t
where letterA > letterB and
      not exists (select 1 from t t2 where t2.letterA = t.letterB and t2.letterB = t.letterA);

select distinct (case when letterA <= letterB then letterA else letterB end) as letterA,
       (case when letterA > letterB then letterA else letterB end) as letterB
from t;

如果不关心最后一列的顺序，可以执行以下操作：

select letterA, letterB
from t
where letterA <= letterB
union all
select letterA, letterB
from t
where letterA > letterB and
      not exists (select 1 from t t2 where t2.letterA = t.letterB and t2.letterB = t.letterA);

select distinct (case when letterA <= letterB then letterA else letterB end) as letterA,
       (case when letterA > letterB then letterA else letterB end) as letterB
from t;

---

工会将过滤掉重复的。 最低值将在第一列中返回：

SELECT LetterOne, LetterTwo
FROM <table>
WHERE LetterOne < LetterTwo
UNION 
SELECT LetterTwo, LetterOne
FROM <table>
WHERE LetterTwo<=LetterOne

---

工会将过滤掉重复的。 最低值将在第一列中返回：

SELECT LetterOne, LetterTwo
FROM <table>
WHERE LetterOne < LetterTwo
UNION 
SELECT LetterTwo, LetterOne
FROM <table>
WHERE LetterTwo<=LetterOne

---

到目前为止你试过什么？发布您的查询，以便我们可以帮助您。@WEI_DBA编辑！您要选择还是删除？@jarlh已选择是否可以按相同顺序复制数据？比如两行，其中LetterOne=A和LetterTwo=b，到目前为止你试过什么？发布您的查询，以便我们可以帮助您。@WEI_DBA编辑！您要选择还是删除？@jarlh已选择是否可以按相同顺序复制数据？就像两行的LetterOne=A和LetterTwo=BGreat一样，我用了你的第二个答案，它成功了。你能解释一下它是如何工作的吗？或者给我指出一个资源的方向吗？太好了，我用了你的第二个答案，它工作了。你能解释一下它是如何工作的吗？或者让我看一下资源的方向吗？这只适用于选择包含双硅酸盐的行，但不包括a | C行这不包括包含D的行这只适用于选择包含双硅酸盐的行，但不包括a | C行这不包括包含D | a的行