Replace a recurring word and the character before it - sql

Question

I am using SQL Server trying to replace each recurring "[BACKSPACE]" in a string and the character that came before the word [BACKSPACE] to mimic what a backspace would do.
Here is my current string:
"This is a string that I would like to d[BACKSPACE]correct and see if I could make it %[BACKSPACE] cleaner by removing the word and $[BACKSPACE] character before the backspace."
Here is what I want it to say:
"This is a string that I would like to correct and see if I could make it cleaner by removing the word and character before the backspace."
Let me make this clearer. In the above example string, the $ and % signs were just used as examples of characters that would need to be removed since they are before the [BACKSPACE] word that I want to replace.
Here is another before example:
The dog likq[BACKSPACE]es it's owner
I want to edit it to read:
The dog likes it's owner
One last before example is:
I am frequesn[BACKSPACE][BACKSPACE]nlt[BACKSPACE][BACKSPACE]tly surprised
I want to edit it to read:
I am frequently surprised

Answer 1

Without a CLR function that provides Regex replacement the only way you'll be able to do this is with iteration in T-SQL. Note, however, that the below solution does not give you the results you ask for, but does the logic you ask. You state that you want to remove the string and the character before, but in 2 of your scenarios that isn't true. For the last 2 strings you remove ' %[BACKSPACE]' and ' $[BACKSPACE]' respectively (notice the leading whitespace).
This leading whitespace is left in this solution. I am not entertaining fixing that, as the real solution is don't use T-SQL for this, use something that supports Regex.
I also assume this string is coming from a column in a table, and said table has multiple rows (with a distinct value for the string on each).
Anyway, the solution:
WITH rCTE AS(
SELECT V.YourColumn,
STUFF(V.YourColumn,CHARINDEX('[BACKSPACE]',V.YourColumn)-1,LEN('[BACKSPACE]')+1,'') AS ReplacedColumn,
1 AS Iteration
FROM (VALUES('"This is a string that I would like to d[BACKSPACE]correct and see if I could make it %[BACKSPACE] cleaner by removing the word and $[BACKSPACE] character before the backspace."'))V(YourColumn)
UNION ALL
SELECT r.YourColumn,
STUFF(r.ReplacedColumn,CHARINDEX('[BACKSPACE]',r.ReplacedColumn)-1,LEN('[BACKSPACE]')+1,''),
r.Iteration + 1
FROM rCTE r
WHERE CHARINDEX('[BACKSPACE]',r.ReplacedColumn) > 0)
SELECT TOP (1) WITH TIES
r.YourColumn,
r.ReplacedColumn
FROM rCTE r
ORDER BY ROW_NUMBER() OVER (PARTITION BY r.YourColumn ORDER BY r.Iteration DESC);
dB<>fiddle

Answer 2

I've had a crack to see if I can get this to work using the traditional tally-table method without any recursion.
I think I have something that works - however the recursive cte version is definitely a cleaner solution and probably better performing, however throwing this in as just an alternative non-recursive way.
/* tally table for use below */
select top 1000 N=Identity(int, 1, 1)
into dbo.Digits
from master.dbo.syscolumns a cross join master.dbo.syscolumns
with w as (
select seq = Row_Number() over (order by t.N),
part = Replace(Substring(#string, t.N, CharIndex(Left(#delimiter,1), #string + #delimiter, t.N) - t.N),Stuff(#delimiter,1,1,''),'')
from Digits t
where t.N <= DataLength(#string)+1 and Substring(Left(#delimiter,1) + #string, t.N, 1) = Left(#delimiter,1)
),
p as (
select seq,Iif(Iif(Lead(part) over(order by seq)='' and lag(part) over(order by seq)='',1,0 )=1 ,'', Iif( seq<Max(seq) over() and part !='',Left(part,Len(part)-1),part)) part
from w
)
select result=(
select ''+ part
from p
where part!=''
order by seq
for xml path('')
)

Answer 3

Here's a simple RegEx pattern that should work:
/.\[BACKSPACE\]/g
EDIT
I have no way to test this right now on my chromebook, but this seems like it should work for T-SQL in the LIKE clause
LIKE '_\[BACKSPACE]' ESCAPE '\'