SQL Server: String insertion by position - sql-server

Question

I want to insert a set of values into a given string at specified positions. I couldn't find an existing solution for this so I created the following query which does so. I am wondering if there is a way to simplify it, especially the portion which queries the cte and creates the NewString. Also, is there a way to construct the cte recursion without involving the ID column? The ID (and the rest) seems to work fine, just wondering if it could be tweaked to make it more organic/elegant or if there is a better solution overall. The different groups are really only for testing purposes; each group corresponds to a possible insertion position scenario. Thus, there will not be groups involved when I use it.
declare
#String varchar(200),
#StringLen int,
#GroupID int,
#PositionMax int
declare #Chars table (
ID int identity,
GroupID int,
Position int,
Value varchar(20)
)
select
#String = 'abcde',
#StringLen = len(#String),
#GroupID = 1
--Affix
--[P]refix
--[I]nfix
--[S]uffix
insert #Chars
select
GroupID,
Position,
Value
from (
values
(1, 0, 'X'), --P
(2, 2, 'Y'), --I
(3, 5, 'Z'), --S
(4, 0, 'X'), --P
(4, 2, 'Y'), --I
(5, 2, 'Y'), --I
(5, 5, 'Z'), --S
(6, 0, 'X'), --P
(6, 5, 'Z'), --S
(7, 0, 'X'), --P
(7, 2, 'Y'), --I
(7, 5, 'Z'), --S
(8, 2, 'Y1'), --I
(8, 4, 'Y2'), --I
(9, 0, 'X'), --P
(9, 2, 'Y1'), --I
(9, 4, 'Y2'), --I
(10, 2, 'Y1'), --I
(10, 4, 'Y2'), --I
(10, 5, 'Z'), --S
(11, 0, 'X'), --P
(11, 2, 'Y1'), --I
(11, 4, 'Y2'), --I
(11, 5, 'Z') --S
) as T(GroupID, Position, Value)
order by GroupID, Position
;with cte (
ID,
GroupID,
LeftString,
Value,
RightString,
Position
) as (
select
ID,
GroupID,
LeftString,
Value,
RightString,
Position
from (
select
row_number() over (partition by GroupID order by ID) as RowNumber,
ID,
GroupID,
cast(left(#String, Position) as varchar(200)) as LeftString,
Value,
cast(right(#String, #StringLen - Position) as varchar(200)) as RightString,
Position
from #Chars
) as C
where RowNumber = 1
union all
select
vc.ID,
vc.GroupID,
cast(left(RightString, vc.Position - cte.Position) as varchar(200)) as LeftString,
vc.Value,
cast(right(RightString, #StringLen - vc.Position) as varchar(200)) as RightString,
vc.Position
from #Chars vc
join cte cte
on cte.GroupID = vc.GroupID
and cte.ID + 1 = vc.ID
)
select
GroupID,
case
when LSLenSumMax < #StringLen
then NewString + RightString
else NewString
end as NewString
from (
select
GroupID,
max(LSLenSum) as LSLenSumMax,
RightString,
stuff((
select
LeftString + Value
from cte cte
where cte.GroupID = cteLR.GroupID
for xml path(''), type
).value('(./text())[1]', 'varchar(max)'), 1, 0, '') as NewString
from (
select
GroupID,
(select sum(len(LeftString)) from cte cteL where cteL.groupID = cte.groupID) as LSLenSum,
(select top 1 RightString from cte cteR where cteR.groupID = cte.groupID order by cteR.ID desc) as RightString
from cte cte
) as cteLR
group by
GroupID,
RightString
) as C
order by GroupID

Answer 1

You can implement a custom
aggregate function... Or try this: A recursive scalar function:
CREATE FUNCTION dbo.GetPrefixTo (#GroupID INT, #Position INT, #String CHAR(200))
RETURNS Char(200)
WITH EXECUTE AS CALLER
AS
BEGIN
DECLARE #str CHAR(200) = NULL
DECLARE #beforePosition INT = 0
IF (SELECT COUNT(*) FROM Chars WHERE GroupID = #GroupID AND Position < #Position) > 0
BEGIN
SELECT #beforePosition = MAX(Position) FROM chars WHERE GroupID = #GroupID AND Position < #Position
select #str = RTRIM(dbo.GetPrefixTo(#GroupID, #beforePosition, substring(#String, 1, #Position))) +
+ RTrim(Value) + substring(#String, #Position + 1, len(#string) + 1)
FROM Chars WHERE GroupID = #GroupID AND Position = #Position
END
ELSE
SELECT #str = substring(#String, 1, #Position) + RTrim(Value) + substring(#String, #Position + 1, len(#string) + 1) FROM Chars
WHERE GroupID = #GroupID AND Position = #Position
RETURN #str
END
And group by GroupID and aggregate max(position):
SELECT groupID, max(Position)
, dbo.GetPrefixTo(groupID, max(Position), 'abcde')
FROM Chars
GROUP BY GroupID
This is the result:
1 0 Xabcde
2 2 abYcde
3 5 abcdeZ
4 2 XabYcde
5 5 abYcdeZ
6 5 XabcdeZ
7 5 XabYcdeZ
8 4 abY1cdY2e
9 4 XabY1cdY2e
10 5 abY1cdY2eZ
11 5 XabY1cdY2eZ
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