SQL - Replacing all "ASCII/special characters" in a string - sql

Question

Edit: I have about 80 characters that are causing problems in my application so I don't want to hard code a REPLACE for every single character. I think it would be easier to create a separate table with two columns,"special characters" and "replacement characters", and I will remove those columns from the original table which contains the column "StringTest". My goal will be figuring out how to use the characters table to replace characters in the string table.
I am trying to replace all "special characters" (ie À, Æ, Ç) with "MappedCharacters" (A, AE, C) in SQL Server. I have tried two different techniques, one using a cursor, one without a cursor, to search through a string and replace all special characters with mapped characters. Each of my methods only replaces characters they are in the same row as the string.
Example before:
num SpecialCharacter MappedCharacter StringTest
1 À A StringÀÆ
2 Æ AE ÆStringÆ
3 Ç C StrÇÀing
Example after:
num SpecialCharacter MappedCharacter StringTest
1 À A StringAÆ
2 Æ AE AEStringAE
3 Ç C StrCÀing
Preferred Output:
num SpecialCharacter MappedCharacter StringTest
1 À A StringAAE
2 Æ AE AEStringAE
3 Ç C StrCAing
So you can see that I want to replace all "special characters" in StringTest but only characters that are in the same row are getting replaced.
I haven't quite figured out how to do that just yet.
Here are the two SQL code that I have been trying to modify (I only need one to work)
First Method:
DECLARE #cASCIINum INT;
DECLARE #cSpecialChar VARCHAR(50);
DECLARE #cMappedChar VARCHAR(50);
DECLARE #cStringTest VARCHAR(50);
DECLARE #mapCursor as CURSOR;
SET #mapCursor = CURSOR FOR
SELECT [ASCIINum]
,[SpecialChar]
,[MappedChar]
,[StringTest]
FROM [intranet].[dbo].[CharMapTestTab];
OPEN #mapCursor;
FETCH NEXT FROM #mapCursor INTO #cASCIINum,
#cSpecialChar,
#cMappedChar,
#cStringTest;
WHILE ##FETCH_STATUS = 0
BEGIN
UPDATE [intranet].[dbo].[CharMapTestTab]
SET StringTest = REPLACE(StringTest, SpecialChar, MappedChar)
WHERE SpecialChar <> MappedChar
END
CLOSE #mapCursor;
DEALLOCATE #mapCursor;
Second Method:
DECLARE #ASCIINum INT = 0
WHILE (1 = 1)
BEGIN
SELECT #ASCIINum = ASCIINum
FROM [intranet].[dbo].[CharMapTestTab]
WHERE ASCIINum > #ASCIINum
ORDER BY ASCIINum
IF ##ROWCOUNT = 0 BREAK;
UPDATE [intranet].[dbo].[CharMapTestTab]
SET StringTest = REPLACE(StringTest, SpecialChar, MappedChar)
WHERE SpecialChar <> MappedChar
SELECT TOP 1000 [ASCIINum]
,[SpecialChar]
,[MappedChar]
,[StringTest]
FROM [intranet].[dbo].[CharMapTestTab]
END

Answer 1

Try this, it works better than looping because there is only 1 update:
-- create test table vc
create table vc(StringTest varchar(20))
insert vc values('StringÀÆ'), ('ÆStringÆ')
go
-- create test table CharacterMapping
create table CharacterMapping(SpecialCharacter char(1), MappedCharacter varchar(2))
insert CharacterMapping values('À', 'A'),('Æ', 'AE'), ('Ç', 'C')
go
--build the varchar for updating
declare #x varchar(max) = 'StringTest'
select #x = 'replace('+#x+', ''' + SpecialCharacter + ''','''+MappedCharacter+''')'
from CharacterMapping
set #x = 'update vc set StringTest=' + #x +' from vc'
exec (#x)
select * from vc
Result:
StringAAE
AEStringAE

Answer 2

I would make a separate mapping table which contains the bad character and its corresponding good character, one set per row. Then loop over that table and do a replace for each character set.
DECLARE #map TABLE (
id INT,
badChar CHAR,
goodChar CHAR
)
DECLARE #strings TABLE (
searchString VARCHAR(50)
)
INSERT INTO #map
VALUES
(1, 'y', 'a'),
(2, 'z', 'b')
DECLARE #curRow INT, #totalRows INT
SET #curRow = 1
SELECT #totalRows = COUNT(*) FROM #map
INSERT INTO #strings
VALUES
('zcccyccz'),
('cccyccz')
WHILE #curRow <= #totalRows
BEGIN
UPDATE #strings
SET searchString = REPLACE(searchString, badChar, goodChar)
FROM #map
WHERE id = #curRow
SET #curRow = #curRow + 1
END
SELECT * FROM #strings
--Output
--bcccaccb
--cccaccb

Answer 3

It would be helpful to know how many rows are in your table and how many you estimate to have "special characters". Also, are there only 3 special characters? if you have 40 or less special characters, it may look ridiculous, but I'd just nest as many REPLACE() calls as you have special characters, like:
UPDATE YourTable SET YourColumn = REPLACE(
REPLACE(
REPLACE(YourColumn,'Ç','C')
,'Æ','AE')
,'À','A')
if most rows have special characters, I'd skip any WHERE. if only a few rows have special characters, I'd use a CTE to identify them:
;WITH AllSpecialRows AS
(
SELECT PrimaryKey FROM YourTable WHERE YourColumn LIKE '%À%'
UNION
SELECT PrimaryKey FROM YourTable WHERE YourColumn LIKE '%Æ%'
UNION
SELECT PrimaryKey FROM YourTable WHERE YourColumn LIKE '%Ç%'
)
UPDATE y
SET YourColumn = REPLACE(
REPLACE(
REPLACE(YourColumn,'Ç','C')
,'Æ','AE')
,'À','A')
FROM YourTable y
INNER JOIN AllSpecialRows s ON y.PrimaryKey =s.PrimaryKey

Answer 4

update table
set column = REPLACE(column,'À','A')
where column like ('%À%')
update table
set column = REPLACE(column,'Æ','AE')
where column like ('%Æ%')
I will leave the 3rd to you
Or this might be more efficient
update table
set column = REPLACE(REPLACE(column,'À','A'),'Æ','AE')
where column like ('%À%')
or column like ('%Æ%')
If you really want to process a list of mapped characters then this is not a proper answer

Answer 5

#t-clausen.dk answer with Table variables and temp tables, just to avoid people mess up their dev databases with additional tables.
TABLE Variables:
-- Create test table variable #CharacterMapping
DECLARE #CharacterMapping TABLE (SpecialCharacter char(1), MappedCharacter varchar(2))
INSERT #CharacterMapping VALUES('À', 'A'), ('Æ', 'AE'), ('Ç', 'C')
--Build the varchar for updating
DECLARE #x varchar(max) = 'StringTest'
SELECT #x = 'replace('+#x+', ''' + SpecialCharacter + ''',''' + MappedCharacter + ''')'
FROM #CharacterMapping
SET #x = 'DECLARE #vc TABLE(StringTest varchar(20));'
+ ' insert #vc values(''StringÀÆ''), (''ÆStringÆ'');'
+ 'update #vc set StringTest=' + #x +' from #vc;'
+ 'SELECT * FROM #vc;'
Exec (#x)
GO
With Temp table:
-- Create test temp table #vc
CREATE TABLE #vc(StringTest varchar(20))
INSERT #vc VALUES('StringÀÆ'), ('ÆStringÆ')
-- Create test table CharacterMapping
DECLARE #CharacterMapping TABLE (SpecialCharacter char(1), MappedCharacter varchar(2))
INSERT #CharacterMapping VALUES('À', 'A'), ('Æ', 'AE'), ('Ç', 'C')
--Build the varchar for updating
DECLARE #x varchar(max) = 'StringTest'
SELECT #x = 'replace('+#x+', ''' + SpecialCharacter + ''',''' + MappedCharacter + ''')'
FROM #CharacterMapping
SET #x = 'update #vc set StringTest=' + #x +' from #vc'
-- Execute
EXEC (#x)
-- Select the results
SELECT * FROM #vc;
-- Drop temp table
DROP TABLE #vc;
GO