Question

What is the best way to remove all spaces from a string in SQL Server 2008?

LTRIM(RTRIM(' a b ')) would remove all spaces at the right and left of the string, but I also need to remove the space in the middle.

Answer 1

Simply replace it;

SELECT REPLACE(fld_or_variable, ' ', '')

Edit:
Just to clarify; its a global replace, there is no need to trim() or worry about multiple spaces for either char or varchar:

create table #t (
    c char(8),
    v varchar(8))

insert #t (c, v) values 
    ('a a'    , 'a a'    ),
    ('a a  '  , 'a a  '  ),
    ('  a a'  , '  a a'  ),
    ('  a a  ', '  a a  ')

select
    '"' + c + '"' [IN], '"' + replace(c, ' ', '') + '"' [OUT]
from #t  
union all select
    '"' + v + '"', '"' + replace(v, ' ', '') + '"'
from #t 

Result

IN             OUT
===================
"a a     "     "aa"
"a a     "     "aa"
"  a a   "     "aa"
"  a a   "     "aa"
"a a"          "aa"
"a a  "        "aa"
"  a a"        "aa"
"  a a  "      "aa"