slugify function for MySQL

fn.slugify.sql

/* 
The MIT License (MIT)

Copyright (c) 2014 jose reis<jose.reis@artbit.pt>

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

Credits:
- http://stackoverflow.com/questions/5409831/mysql-stored-function-to-create-a-slug

*/

DELIMITER ;;

DROP FUNCTION IF EXISTS `slugify`;;
CREATE FUNCTION `slugify`(dirty_string varchar(255)) RETURNS varchar(255) CHARSET utf8
    DETERMINISTIC
BEGIN
    DECLARE x, y , z , k INT;
    DECLARE temp_string, new_string, accents, noAccents VARCHAR(255);
    DECLARE is_allowed BOOL;
    DECLARE c, check_char VARCHAR(1);

    -- IF NULL DO NOT PROCEED
    If dirty_string IS NULL Then
        return dirty_string;
    End If;

    set temp_string = LOWER(dirty_string);

    -- REPLACE ACCENTS
    -- WITH CAPS
    -- set accents = 'ŠšŽžÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÑÒÓÔÕÖØÙÚÛÜÝŸÞàáâãäåæçèéêëìíîïñòóôõöøùúûüýÿþƒ';
    -- set noAccents = 'SsZzAAAAAAACEEEEIIIINOOOOOOUUUUYYBaaaaaaaceeeeiiiinoooooouuuuyybf';
    -- ONLY SMALL CAPS
    set accents = 'šžàáâãäåæçèéêëìíîïñòóôõöøùúûüýÿþƒ';
    set noAccents = 'szaaaaaaaceeeeiiiinoooooouuuuyybf';
    set k = CHAR_LENGTH(accents);

    while k > 0 do
        set temp_string = REPLACE(temp_string, SUBSTRING(accents, k, 1), SUBSTRING(noAccents, k, 1));
        set k = k - 1;
    end while;

    -- CONVERT & TO EMPTY SPACE
    Set temp_string = REPLACE(temp_string, '&', '');

    -- REPLACE ALL UNWANTED CHARS
    Select temp_string REGEXP('[^a-z0-9\-]+') into x;
    If x = 1 then
        set z = 1;
        set k = CHAR_LENGTH(temp_string);
        While z <= k Do
            Set c = SUBSTRING(temp_string, z, 1);
            Set is_allowed = FALSE;
            If !((ascii(c) = 45) or (ascii(c) >= 48 and ascii(c) <= 57) or (ascii(c) >= 97 and ascii(c) <= 122)) Then
                Set temp_string = REPLACE(temp_string, c, '-');
            End If;
            set z = z + 1;
        End While;
    End If;

    Select temp_string REGEXP("^-|-$|'") into x;
    If x = 1 Then
        Set temp_string = Replace(temp_string, "'", '');
        Set z = CHAR_LENGTH(temp_string);
        Set y = CHAR_LENGTH(temp_string);
        Dash_check: While z > 1 Do
            If STRCMP(SUBSTRING(temp_string, -1, 1), '-') = 0 Then
                Set temp_string = SUBSTRING(temp_string,1, y-1);
                Set y = y - 1;
            Else
                Leave Dash_check;
            End If;
            Set z = z - 1;
        End While;
    End If;

    Repeat
        Select temp_string REGEXP("--") into x;
        If x = 1 Then
            Set temp_string = REPLACE(temp_string, "--", "-");
        End If;
    Until x <> 1 End Repeat;

    If LOCATE('-', temp_string) = 1 Then
        Set temp_string = SUBSTRING(temp_string, 2);
    End If;

    Return temp_string;
END;;

DELIMITER ;