I'd Like To Have Characters Only (no Signs, Numbers And Spaces At All)

It should be done with SQLite just like this; yes, I know, it is quite easy task, If I use UDF(User Define Function). but, I have severe difficulty with it. so, looking for anothe

Solution 1:

I believe that you could base the resolution on :-

WITHRECURSIVE eachchar(counter,rowid,c,rest) AS (
        SELECT1,rowid,'',mycolumn AS rest FROM mytable
        UNIONALLSELECT counter+1,rowid,substr(rest,1,1),substr(rest,2) FROM eachchar WHERE length(rest) >0 LIMIT 100
    )
SELECT group_concat(c,'') AS mycolumn, myothercolumn, mycolumn AS original
FROM eachchar JOIN mytable ON eachchar.rowid = mytable.rowid 
WHERE length(c) >0AND (
        unicode(c) BETWEEN unicode('a') AND unicode('z') 
        OR unicode(c) BETWEEN unicode('A') AND unicode('Z')
    )
GROUPBY rowid;

Demo :-

Perhaps consider the following :-

/* Create the Test Environment */DROPTABLE IF EXISTS mytable;
CREATETABLE IF NOTEXISTS mytable (mycolumn TEXT, myothercolumn);
/* Add the Testing data */INSERTINTO mytable VALUES
    ('123-abc_"D E F()[]{}~`!@#$%^&*-+=|\?><<:;''','A')
    ,('123-xyz_"X Y Z()[]{}~`!@#$%^&*-+=|\?><<:;''','B')
    ,('123-abc_"A B C()[]{}~`!@#$%^&*-+=|\?><<:;''','C')
;

/* split each character thenconcatenat only the required characters*/WITHRECURSIVE eachchar(counter,rowid,c,rest) AS (
        SELECT1,rowid,'',mycolumn AS rest FROM mytable
        UNIONALLSELECT counter+1,rowid,substr(rest,1,1),substr(rest,2) FROM eachchar WHERE length(rest) >0 LIMIT 100
    )
SELECT group_concat(c,'') AS mycolumn, myothercolumn, mycolumn AS original
FROM eachchar JOIN mytable ON eachchar.rowid = mytable.rowid 
WHERE length(c) >0AND (
        unicode(c) BETWEEN unicode('a') AND unicode('z') 
        OR unicode(c) BETWEEN unicode('A') AND unicode('Z')
    )
GROUPBY rowid;
/* Cleanup Test Environment */DROPTABLE IF EXISTS mytable;

This results in :-