SQL如何使列值向右或向左滑动？

Question

这是一道面试题。

如果我有这样的table：

ID        FirstName       LastName
--        ---------       --------
1         Aaron           Aames
2         Malcolm         Middle
3         Zamon           Zorr

我怎样才能得到这样的输出？

          Aaron           Aames
          Aames           Malcolm
          Malcolm         Middle
          Middle          Zamon
          Zamon           Zorr

注意：如果您需要特定的方言，请使用 T-SQL。

Answer 1

你的声望很高，所以这不只是一个"they asked me at an interview"类的问题。

有几种方法。我认为我会选择 union all。认识到每隔一行来自 table。其余的是从一行到另一行。所以，这表明：

select firstname, lastname
from likethis t
union all
select t.lastname, lead(t.firstname) over (order by id)
from likethis t

唉，这给你六行而不是五行，所以最后一行需要被过滤掉：

select firstname, lastname
from (select firstname, lastname
      from likethis t
      union all
      select t.lastname, lead(t.firstname) over (order by id)
      from likethis t
     ) t
where lastname is not null
order by firstname;

注意：我无法确定排序标准是按字母顺序还是按 id；这些解决方案假定它是按字母顺序排列的。

第二个注意事项：我猜这不是他们想要的解决方案。他们可能正在寻找自我加入。但是，当 lead() 为您完成工作时，为什么还要麻烦。

Answer 2

这是使用自连接的另一种方法。

CREATE TABLE temp (ID INT IDENTITY, FirstName VARCHAR(25), LastName VARCHAR(25));

INSERT INTO temp VALUES 
(N'Aaron', N'Aames'),
(N'Malcolm', N'Middle'),
(N'Zamon', N'Zorr');

WITH names(ID, Name, ColNum) AS(
    SELECT
        ID, FirstName, 1
    FROM temp
    UNION ALL
    SELECT
        ID, LastName, 2
    FROM temp
),
numbered AS(
    SELECT
        rn = ROW_NUMBER() OVER(ORDER BY ID, ColNum),
        Name
    FROM names
)
SELECT
    n.Name AS Name1, n2.Name AS Name2
FROM numbered n
INNER JOIN numbered n2
    ON n.rn = n2.rn - 1

DROP TABLE temp

http://sqlfiddle.com/#!3/d91c4/2

Answer 3

我觉得可以这样解决：

SELECT
    t.LastName AS FirstName, t2.FirstName AS LastName
FROM    
    t
    INNER JOIN t as t2 ON t2.ID - 1 = t.ID
UNION
SELECT 
    t3.FirstName, t3.LastName 
FROM t AS t3

据我检查正确，它应该按以下方式提供最终结果集：

Aaron     Aames       <=  originates from t3:  where t3.ID = 1 
Aames     Malcolm     <=  originates from (t1, t2) Join:  where t2.ID = 2 and t.ID = 1
Malcolm   Middle      <=  originates from t3:  where t3.ID = 2
Middle    Zamon       <=  originates from (t1, t2) Join:  where t2.ID = 3 and t.ID = 2
Zamon     Zorr        <=  originates from t3:  where t3.ID = 3

SQL如何使列值向右或向左滑动？

How do you make a column value slide to the right or the left using SQL?

sql

sql-server