How to remove accents and all chars <> a..z in sql-server?

The best way to achieve this is very simple and efficient :

SELECT 'àéêöhello!' Collate SQL_Latin1_General_CP1253_CI_AI

which outputs 'aeeohello!'

The string must not be unicode. If you have a nvarchar just cast it to varchar before using the collate.

Here is a function that answers the OP needs :

create function [dbo].[RemoveExtraChars] ( @p_OriginalString varchar(50) )
returns varchar(50) as
begin

  declare @i int = 1;  -- must start from 1, as SubString is 1-based
  declare @OriginalString varchar(100) = @p_OriginalString Collate SQL_Latin1_General_CP1253_CI_AI;
  declare @ModifiedString varchar(100) = '';

  while @i <= Len(@OriginalString)
  begin
    if SubString(@OriginalString, @i, 1) like '[a-Z]'
    begin
      set @ModifiedString = @ModifiedString + SubString(@OriginalString, @i, 1);
    end
    set @i = @i + 1;
  end

  return @ModifiedString

end

Then, the command:

select dbo.RemoveExtraChars('aèàç=.32s df')

outputs

aeacsdf

You can avoid hard-coded REPLACE statements by using a COLLATE clause with an accent-insensitive collation to compare the accented alphabetic characters to non-alphabetic ones:

DECLARE 
  @s1 NVARCHAR(200),
  @s2 NVARCHAR(200)

SET @s1 = N'aèàç=.32s df' 

SET @s2 = N''
SELECT @s2 = @s2 + no_accent 
FROM ( 
  SELECT 
    SUBSTRING(@s1, number, 1) AS accent,
    number
  FROM master.dbo.spt_values 
  WHERE TYPE = 'P'
  AND number BETWEEN 1 AND LEN(@s1) 
) s1 
INNER JOIN (
  SELECT NCHAR(number) AS no_accent
  FROM master.dbo.spt_values 
  WHERE type = 'P'
  AND (number BETWEEN 65 AND 90 OR number BETWEEN 97 AND 122) 
) s2 
  ON s1.accent COLLATE LATIN1_GENERAL_CS_AI = s2.no_accent 
ORDER BY number

SELECT @s1 
SELECT @s2 

/*
aèàç=.32s df
aeacsdf
*/

    SELECT 'áéíóú' COLLATE Cyrillic_General_CI_AI

This will replace all accented chars...

result: aeiou

Hope this help you!

Let me clarify something first: the accented characters you show are not actually Unicode (as one answer implies); these are 8-bit ASCII characters. One thing to keep in mind: you see characters like è and à simply because this is how your code page (the code page used by your OS and/or SQL Server [I'm not sure which one]) displays them. In a different code page, these characters would be represented by totally different symbols (e.g. if you use a Cyrillic or Turkish code page).

Anyway, say you want to replace these 8-bit chars with the closest US/Latin character equivalent for your default code page [I assume these are characters from some variation of a Latin character set]. This is how I approached a similar problem (disclaimer: this is not a very elegant solution, but I could not think of anything better at the time):

Create a UDF to translate an 8-bit ASCII character to a 7-bit printable ASCII equivalent, such as:

CREATE FUNCTION dbo.fnCharToAscii
(
  @Char AS VARCHAR
)
RETURNS
  VARCHAR   
AS
BEGIN
IF (@Char IS NULL)
  RETURN ''

-- Process control and DEL chars.
IF (ASCII(@Char) < 32) OR (ASCII(@Char) = 127)
    RETURN ''

-- Return printable 7-bit ASCII chars as is.
-- UPDATE TO DELETE NON-ALPHA CHARS.
IF (ASCII(@Char) >= 32) AND (ASCII(@Char) < 127)
    RETURN @Char

-- Process 8-bit ASCII chars.
RETURN
  CASE ASCII(@Char)
    WHEN 128 THEN 'E'
    WHEN 129 THEN '?'
    WHEN 130 THEN ','
    WHEN 131 THEN 'f'
    WHEN 132 THEN ','
    WHEN 133 THEN '.'
    WHEN 134 THEN '+'
    WHEN 135 THEN '+'
    WHEN 136 THEN '^'
    WHEN 137 THEN '%'
    WHEN 138 THEN 'S'
    WHEN 139 THEN '<'
    WHEN 140 THEN 'C'
    WHEN 141 THEN '?'
    WHEN 142 THEN 'Z'
    WHEN 143 THEN '?'
    WHEN 144 THEN '?'
    WHEN 145 THEN ''''
    WHEN 146 THEN ''''
    WHEN 147 THEN '"'
    WHEN 148 THEN '"'
    WHEN 149 THEN '-'
    WHEN 150 THEN '-'
    WHEN 151 THEN '-'
    WHEN 152 THEN '~'
    WHEN 153 THEN '?'
    WHEN 154 THEN 's'
    WHEN 155 THEN '>'
    WHEN 156 THEN 'o'
    WHEN 157 THEN '?'
    WHEN 158 THEN 'z'
    WHEN 159 THEN 'Y'
    WHEN 160 THEN ' '
    WHEN 161 THEN 'i'
    WHEN 162 THEN 'c'
    WHEN 163 THEN 'L'
    WHEN 164 THEN '?'
    WHEN 165 THEN 'Y'
    WHEN 166 THEN '|'
    WHEN 167 THEN '$'
    WHEN 168 THEN '^'
    WHEN 169 THEN 'c'
    WHEN 170 THEN 'a'
    WHEN 171 THEN '<'
    WHEN 172 THEN '-'
    WHEN 173 THEN '-'
    WHEN 174 THEN 'R'
    WHEN 175 THEN '-'
    WHEN 176 THEN 'o'
    WHEN 177 THEN '+'
    WHEN 178 THEN '2'
    WHEN 179 THEN '3'
    WHEN 180 THEN ''''
    WHEN 181 THEN 'm'
    WHEN 182 THEN 'P'
    WHEN 183 THEN '-'
    WHEN 184 THEN ','
    WHEN 185 THEN '1'
    WHEN 186 THEN '0'
    WHEN 187 THEN '>'
    WHEN 188 THEN '?'
    WHEN 189 THEN '?'
    WHEN 190 THEN '?'
    WHEN 191 THEN '?'
    WHEN 192 THEN 'A'
    WHEN 193 THEN 'A'
    WHEN 194 THEN 'A'
    WHEN 195 THEN 'A'
    WHEN 196 THEN 'A'
    WHEN 197 THEN 'A'
    WHEN 198 THEN 'A'
    WHEN 199 THEN 'C'
    WHEN 200 THEN 'E'
    WHEN 201 THEN 'E'
    WHEN 202 THEN 'E'
    WHEN 203 THEN 'E'
    WHEN 204 THEN 'I'
    WHEN 205 THEN 'I'
    WHEN 206 THEN 'I'
    WHEN 207 THEN 'I'
    WHEN 208 THEN 'D'
    WHEN 209 THEN 'N'
    WHEN 210 THEN 'O'
    WHEN 211 THEN 'O'
    WHEN 212 THEN 'O'
    WHEN 213 THEN 'O'
    WHEN 214 THEN 'O'
    WHEN 215 THEN 'x'
    WHEN 216 THEN 'O'
    WHEN 217 THEN 'U'
    WHEN 218 THEN 'U'
    WHEN 219 THEN 'U'
    WHEN 220 THEN 'U'
    WHEN 221 THEN 'Y'
    WHEN 222 THEN 'b'
    WHEN 223 THEN 'B'
    WHEN 224 THEN 'a'
    WHEN 225 THEN 'a'
    WHEN 226 THEN 'a'
    WHEN 227 THEN 'a'
    WHEN 228 THEN 'a'
    WHEN 229 THEN 'a'
    WHEN 230 THEN 'a'
    WHEN 231 THEN 'c'
    WHEN 232 THEN 'e'
    WHEN 233 THEN 'e'
    WHEN 234 THEN 'e'
    WHEN 235 THEN 'e'
    WHEN 236 THEN 'i'
    WHEN 237 THEN 'i'
    WHEN 238 THEN 'i'
    WHEN 239 THEN 'i'
    WHEN 240 THEN 'o'
    WHEN 241 THEN 'n'
    WHEN 242 THEN 'o'
    WHEN 243 THEN 'o'
    WHEN 244 THEN 'o'
    WHEN 245 THEN 'o'
    WHEN 246 THEN 'o'
    WHEN 247 THEN '-'
    WHEN 248 THEN 'o'
    WHEN 249 THEN 'u'
    WHEN 250 THEN 'u'
    WHEN 251 THEN 'u'
    WHEN 252 THEN 'u'
    WHEN 253 THEN 'y'
    WHEN 254 THEN 'b'
    WHEN 255 THEN 'y'
  END
RETURN ''
END

The code above is general-purpose, so you can adjust the character mappings to remove all non-alphabetic characters, e.g. you can use code like this in the match for printable 7-bit ASCII character (this assumes case-insensitive collation):

IF @Char NOT LIKE '[a-z]' RETURN ''

To see if your character mapping for 8-bit ASCII symbols works correctly, run the following code:

DECLARE @I   INT
DECLARE @Msg VARCHAR(32)

SET @I = 128

WHILE @I < 256
BEGIN
    SELECT @Msg = CAST(@I AS VARCHAR) + 
    ': ' + 
    CHAR(@I) + 
    '=' + 
    dbo.fnCharToAscii(CHAR(@I))
    PRINT @Msg
    SET @I = @I + 1 
END

Now you can create a UDF to process a string:

CREATE FUNCTION dbo.fnStringToAscii
(
  @Value AS VARCHAR(8000)
)
RETURNS
  VARCHAR(8000) 
AS
BEGIN
IF (@Value IS NULL OR DATALENGTH(@Value) = 0)
  RETURN ''

DECLARE @Index  INT
DECLARE @Result VARCHAR(8000)

SET @Result = ''
SET @Index  = 1

WHILE (@Index <= DATALENGTH(@Value))
BEGIN
  SET @Result = @Result + dbo.fnCharToAscii(SUBSTRING(@Value, @Index, 1))
  SET @Index = @Index + 1   
END

RETURN @Result
END
GO