SQL script for removing extra characters - sql

Question

I've got MSSQL 2012 database with some data issues in the certain column A which contains text.
There are many occurences of aditional unnecesarry character after the </B> tag, for instance:
'<B>Something</B>g' where should stand '<B>Something</B>'
'<B>SomethingElse</B>e' where should stand '<B>SomethingElse</B>'
Previous values are part of a greater text, for instance and can occur more than once -> Column example:
'Some text is here <B>Something</B>g and also here <B>SomethingElse</B>e more text'
Those 'extra' characters are always the same as the last character between the <B></B> tags.
I would like to create SQL scripts which will:
Remove extra character after </B> tag
Only if extra character is the same as the last character between the
<B></B> tags (as a aditional check). EDIT: This is not absolutely necessary
I assuming there is a way of calling replace function, like in this pseudo in which X represents any character.
replace(X</B>X, X</B>);
But I am not very good in SQL and also I don't know how to implement 2. check.
Thank you for your help.

Answer 1

If your column has no other characters then just those strings, you could use this update statement on column a:
update mytable
set a = left(a, len(a)-1)
where left(right(a, 6), 5) = right(a, 1) + '</B>'
Here are some test cases in a fiddle.
To replace such occurrences in longer strings, where there might be multiple of them, then you can use this recursive query:
WITH recursive AS (
SELECT replace(a, '</B>', 'µ') as a
FROM mytable
UNION ALL
SELECT stuff(a, charindex('µ', a),
CASE WHEN substring(a, charindex('µ', a)-1, 1)
= substring(a, charindex('µ', a)+1, 1)
THEN 2
ELSE 1
END, '</B>')
FROM recursive
WHERE charindex('µ', a) > 0
)
SELECT *
FROM recursive
WHERE charindex('µ', a) = 0
The character µ that appears in several places should be a character that you do not expect to ever have in your data. Replace it by another character if necessary.
Here is a fiddle.
The above query turned into an update statement looks like below. It assumes that your table has a primary key id:
WITH recursive AS (
SELECT id,
replace(a, '</B>', 'µ') as a,
0 as modified
FROM mytable
UNION ALL
SELECT id,
stuff(a, charindex('µ', a),
CASE WHEN substring(a, charindex('µ', a)-1, 1)
= substring(a, charindex('µ', a)+1, 1)
THEN 2 ELSE 1 END, '</B>'),
1
FROM recursive
WHERE charindex('µ', a) > 0
)
UPDATE mytable
SET a = recursive.a
FROM recursive
INNER JOIN mytable
ON mytable.id = recursive.id
WHERE charindex('µ', recursive.a) = 0
AND recursive.modified = 1;
Here is the fiddle for that as well.

Answer 2

You can create a scalar function:
CREATE FUNCTION [dbo].[RemoveChars]
(
-- Add the parameters for the function here
#InputStr NVARCHAR(50)
)
RETURNS NVARCHAR(50)
AS
BEGIN
DECLARE #SearchStr NVARCHAR(4) = '</B>'
DECLARE #LastChar CHAR(1)
DECLARE #LastCharInStr CHAR(1)
DECLARE #Result NVARCHAR(50)
SET #LastChar = SUBSTRING(#InputStr,
CHARINDEX(#SearchStr, #InputStr) + LEN(#SearchStr), 1)
SET #LastCharInStr = SUBSTRING(#InputStr,
CHARINDEX(#SearchStr, #InputStr) - 1, 1)
IF (#LastCharInStr = #LastChar)
SET #Result = SUBSTRING(#InputStr, 0,
CHARINDEX(#SearchStr, #InputStr) + LEN(#SearchStr))
ELSE
SET #Result = #InputStr
RETURN #Result
END
And then call it:
UPDATE MyTable
Set A = dbo.RemoveChars(A)
Personally I would create a second function to only apply the updates to the values that have a difference between the last char in the string and the char after the but that's for you to decide.