成对反转 SQL

Question

我是 SQL 的新手，我想做这样的事情 :

从

出发

12 34 56 78

至

78 56 34 12

我尝试了reverse函数，但结果是87 65 43 21。

有办法吗？感谢阅读！

Answer 1

我相信 string_split 在这里会有用。这是它可以为您的特定情况做些什么（数字总是在增加）。

select *
  from STRING_SPLIT('12 34 56 78', ' ')
 order by value desc;

dbfiddle

更新。当数字并不总是增加时，您可以执行以下操作

with splitted as(
select value, row_number() over(order by (select null)) rn
  from string_split('12 34 78 56', ' '))

select string_agg(value, ' ') within group(order by rn desc)
  from splitted

dbfiddle

Answer 2

您可以使用 string split 将您的字符串拆分成行，然后 string_agg 以您想要的顺序取回字符串：

select string_agg(value, ' ') within group(order by cast(value as int) desc)
  from string_split('12 34 56 78', ' ')

Fiddle

但是，如果您不希望数字按升序排列，则不应按照其他答案中的建议将 string_split 与 row_number 一起使用，因为无法保证顺序。使用另一个函数代替 string_split，例如 here.

中的 DelimitedSplit8K

您的 select 变为：

select string_agg(Item, ' ') within group(order by ItemNumber desc)
  from DelimitedSplit8K('12 34 56 78', ' ');

DelimitedSplit8K代码：

CREATE FUNCTION [dbo].[DelimitedSplit8K]
--===== Define I/O parameters
        (@pString VARCHAR(8000), @pDelimiter CHAR(1))
RETURNS TABLE WITH SCHEMABINDING AS
 RETURN
--===== "Inline" CTE Driven "Tally Table” produces values from 0 up to 10,000...
     -- enough to cover VARCHAR(8000)
  WITH E1(N) AS (
                 SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL 
                 SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL 
                 SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1
                ),                          --10E+1 or 10 rows
       E2(N) AS (SELECT 1 FROM E1 a, E1 b), --10E+2 or 100 rows
       E4(N) AS (SELECT 1 FROM E2 a, E2 b), --10E+4 or 10,000 rows max
 cteTally(N) AS (--==== This provides the "zero base" and limits the number of rows right up front
                     -- for both a performance gain and prevention of accidental "overruns"
                 SELECT 0 UNION ALL
                 SELECT TOP (DATALENGTH(ISNULL(@pString,1))) ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) FROM E4
                ),
cteStart(N1) AS (--==== This returns N+1 (starting position of each "element" just once for each delimiter)
                 SELECT t.N+1
                   FROM cteTally t
                  WHERE (SUBSTRING(@pString,t.N,1) = @pDelimiter OR t.N = 0) 
                )
--===== Do the actual split. The ISNULL/NULLIF combo handles the length for the final element when no delimiter is found.
 SELECT ItemNumber = ROW_NUMBER() OVER(ORDER BY s.N1),
        Item       = SUBSTRING(@pString,s.N1,ISNULL(NULLIF(CHARINDEX(@pDelimiter,@pString,s.N1),0)-s.N1,8000))
   FROM cteStart s
;

成对反转 SQL

Reverse in SQL by pair

sql

sql-server

reverse