sql server - MS SQl string alphanumeric conversion -

i need convert strings stored in table lower case alphanumeric. after search found way

select lower(cast(replace(cname, substring(cname, patindex('%[^a-za-z0-9]%', cname), 1), '') varchar(15))), nnameid namestable 

where names table namestable(nnameid int indentity, cname varchar(100))

its working fine strings

 'abc pqr' , 'abc pqr 123', 'abc@pqr' , 'abc-pqr' , 'abc*pqr' 

, , returning

 abcpqr, abcpqr123, abcpqr , abcpqr , abcpqr 

respectively.

but strings

 '**abc pqr*' , 'abc pqr 123.' , '&abc@ pqr$' , '@abc- pqr( ' , '*abc*pqr]' 

it returning values

 abc pqr , abcpqr123. , abc@pqr$ , abc-pqr( , abcpqr] 

.

whats going wrong?

also, created following function n t-sql same task

    create function [dbo].[ufnremovespecialchars] (@s varchar(256)) returns varchar(256)    schemabinding     begin        if @s null           return null        declare @s2 varchar(256)        set @s2 = ''        declare @l int        set @l = len(@s)        declare @p int    set @p = 1    while @p <= @l begin       declare @c int       set @c = ascii(substring(@s, @p, 1))       if @c between 48 , 57 or @c between 65 , 90 or @c between 97 , 122          set @s2 = @s2 + char(@c)       set @p = @p + 1       end    if len(@s2) = 0       return null    return @s2    end 

i calling code using,

select lower(dbo.ufnremovespecialchars(cname)) namestable , working fine.

which 1 better approach out of two?