Custom sort order in SQL Server mixed datatypes stored in a varchar

Question

I have this

declare @testtable table (test nvarchar(max))


insert into @testtable (test) values ('1.2.3')
insert into @testtable (test) values ('1.20.3')
insert into @testtable (test) values ('1.19.x')
insert into @testtable (test) values ('1.x.x')
insert into @testtable (test) values ('1.19.3')
insert into @testtable (test) values ('DEC09')
insert into @testtable (test) values ('Plutonium')
insert into @testtable (test) values ('dec09')
insert into @testtable (test) values ('N/A')
insert into @testtable (test) values ('MyTest20')
insert into @testtable (test) values ('20MyTest')
insert into @testtable (test) values ('1.4.18')
insert into @testtable (test) values ('1.4.168')

select * from @testtable
order by test asc;

which outputs

1.19.3
1.19.x
1.2.3
1.20.3
1.4.168
1.4.18
1.x.x
20MyTest
DEC09
dec09
MyTest20
N/A
Plutonium

but I would like the output order to be

1.2.3
1.4.18
1.4.168
1.19.3
1.19.x
1.20.3
1.x.x
20MyTest
DEC09
dec09
MyTest20
Plutonium
N/A

(note that N/A is "magic" and always largest, "version" (ex 1.2.3) always have 3 digits, although one or more digit may be char x to indicate "any digit" which should always be considered largest possible digit)

How do I accomplish this in SQL Server?

Answer 1

select TT.*
from @testtable as TT
order by case when TT.test = 'N/A' then 1 else 0 end,
         case when isnumeric(parsename(test, 3)+'E+00') = 1 then cast(parsename(test, 3) as int) else 99999 end,
         case when isnumeric(parsename(test, 2)+'E+00') = 1 then cast(parsename(test, 2) as int) else 99999 end,
         case when isnumeric(parsename(test, 1)+'E+00') = 1 then cast(parsename(test, 1) as int) else 99999 end,
         test