Question

我有一个表People（First_Name，Last_Name）。此表具有与示例中重复的记录（并非所有行都重复）：

First_Name  Last_Name
John        Smith
Alec        Baldwin
Smith       John
Angelo      Gordon
Mary        Bush
Bush        Mary

如何选择所有不同的人？在查询的最终输出中，John Smith应该只出现一次（如果在最终查询中有John Smith或Smith John，则不会导入。）

谢谢。

Answer 1

只需选择一个订单并将其应用于所有人。然后使用一个无论如何都会消除重复的联合

select FirstName,LastName from People where FirstName <= LastName
union
select LastName,FirstName from People where LastName < FirstName

Answer 2

这是一种使用几乎任何SQL风格的方法。

DECLARE @Names TABLE (
  First_Name VARCHAR(32)
  , Last_Name VARCHAR(32)
)  

INSERT INTO @Names VALUES ('John', 'Smith')
INSERT INTO @Names VALUES ('Alec', 'Baldwin')
INSERT INTO @Names VALUES ('Smith', 'John')
INSERT INTO @Names VALUES ('Angelo', 'Gordon')
INSERT INTO @Names VALUES ('Mary', 'Bush')
INSERT INTO @Names VALUES ('Bush', 'Mary')

使用JOIN

SELECT  n1.*
FROM    @Names n1
        LEFT OUTER JOIN @Names n2 ON n2.First_Name = n1.Last_Name
                                     AND n2.Last_Name = n1.First_Name
                                     AND n2.First_Name < n1.First_Name
WHERE   n2.First_Name IS NULL

或NOT EXISTS

SELECT  n1.*
FROM    @Names n1
WHERE   NOT EXISTS (
          SELECT  *  
          FROM    @Names n2 
          WHERE   n2.First_Name = n1.Last_Name
                  AND n2.Last_Name = n1.First_Name
                  AND n2.First_Name < n1.First_Name
        )

Answer 3

抱歉在第一次尝试时错过了你的问题...

WITH People (Firstname, Lastname)
AS
(
    SELECT 'John' AS Firstname, 'Smith' AS Lastname UNION
    SELECT 'John' AS Firstname, 'Smith' AS Lastname UNION
    SELECT 'Alec' AS Firstname, 'Baldwin' AS Lastname UNION
    SELECT 'Smith' AS Firstname, 'John' AS Lastname UNION
    SELECT 'John' AS Firstname, 'Smith' AS Lastname UNION
    SELECT 'Angelo' AS Firstname, 'Gordon' AS Lastname UNION
    SELECT 'Mary' AS Firstname, 'Bush' AS Lastname UNION
    SELECT 'Bush' AS Firstname, 'Mary' AS Lastname
)
SELECT p1.* FROM People p1 
LEFT OUTER JOIN People p2 ON p2.Firstname = p1.Lastname AND p2.Lastname = p1.Firstname AND p2.Firstname < p1.Firstname 
WHERE p2.Firstname IS NULL

Answer 4

这是一个使用Oracle功能的解决方案。其他类型的SQL将具有相同或非常相似的功能：

SQL> select * from t23
  2  /

FIRST_NAME                     LAST_NAME
------------------------------ ------------------------------
John                           Smith
Alec                           Baldwin
Smith                          John
Angelo                         Gordon
Mary                           Bush
Bush                           Mary

6 rows selected.

SQL> select distinct least(first_name, last_name)
  2                  , greatest(first_name, last_name)
  3  from t23
  4  /

LEAST(FIRST_NAME,LAST_NAME)    GREATEST(FIRST_NAME,LAST_NAME)
------------------------------ ------------------------------
Alec                           Baldwin
Bush                           Mary
John                           Smith
Angelo                         Gordon

SQL>

Answer 5

我认为这可能适用于MS-SQL

从人物中选择*

其中（FirstName +“，”+ LastName）＆lt;＆gt; （LastName +“，”+ FirstName）

Answer 6

另一种消化

临时表：

DECLARE @Names TABLE (
  First_Name VARCHAR(32)
  , Last_Name VARCHAR(32)
)  

INSERT INTO @Names VALUES ('John', 'Smith')
INSERT INTO @Names VALUES ('Alec', 'Baldwin')
INSERT INTO @Names VALUES ('Smith', 'John')
INSERT INTO @Names VALUES ('Angelo', 'Gordon')
INSERT INTO @Names VALUES ('Mary', 'Bush')
INSERT INTO @Names VALUES ('Bush', 'Mary')

使用CASE

SELECT DISTINCT 
    CASE WHEN First_Name <= Last_Name THEN First_Name ELSE Last_Name END AS First_Name,
    CASE WHEN First_Name <= Last_Name THEN Last_Name ELSE First_Name END AS Last_Name
FROM @Names

SQL SELECT多个列中的不同行，忽略列顺序（显着性）

6 个答案: