Some help with SUM function

[slowpoke115]

I've got basic SELECT access on an SQL database which contains a list of switches of these switches computers are connected, I want a way of finding all the spaces where computers arent and then totally the number of spare spaces. There is not a field which has spare spaces so I've wrote my own code for this, I'm just struggling with the total part, this is what I've got so far:

SELECT switch, COUNT(*) as "Servers", 20 - COUNT(*) as "Spare slots" 
from dedicated_servers 
where switch like 'rs%' 
GROUP by switch HAVING COUNT(switch) < 20  
order by Servers;switch like 'rs%' GROUP by switch 
HAVING COUNT(switch)

which provides something like the following (it looks tidier on my screen :-( ):

+-------------+---------+-------------+
| switch      | Servers | Spare slots |
+-------------+---------+-------------+
| rsj14-1.dc |      12 |           8 |
| rsj12-1.dc |      15 |           5 |
| rsi2-2.dc  |      16 |           4 |
| rsj13-1.dc |      16 |           4 |
| rsi2-1.dc  |      16 |           4 |
+-------------+---------+-------------+

So yeah, somewhere I want a total of the spare slots column, which = 22 :-)

I only have SELECT access so creating a new column or something like that isn't really an option. i've found this hard mainly because my sum column isn't part of the DB... Thanks in advance for your help boys n' girls.

[slowpoke115]

I mean total = 25, gosh that was stoopid...

[slowpoke115]

Note... the code is also wrong, think I pasted too much or something, i'm new to these forum things, this is the correct code:

SELECT switch, COUNT(*) as "Servers", 20 - COUNT(*) as "Spare slots" 
from dedicated_servers 
where switch like 'rs%' 
GROUP by switch 
HAVING COUNT(switch) < 20  
order by Servers;

I've just tested this and it works and gives the result I originally wrote of.