>>Use a subselect?
>>
>> Something like - untested
>>

>>select 	Result.Numero,
>>	Result.Latitude, 
>>	Result.Longitude,
>>	Result.Distance 
>>  from
>>
>>	( SELECT Client.Numero,
>>		 Client.Latitude,
>>		 Client.Longitude, 
>>		3958.75586574*ACOS(
>>		 CASE WHEN SIN(@Latitude3/57.2957795130823)*SIN(Client.Latitude/57.2957795130823)+
>>		 COS(@Latitude4/57.2957795130823)*COS(Client.Latitude/57.2957795130823)*
>>		 COS(Client.Longitude/57.2957795130823-@Longitude3/57.2957795130823)<-1
>>		 THEN -1
>>		WHEN SIN(@Latitude5/57.2957795130823)*SIN(Client.Latitude/57.2957795130823)+
>>		COS(@Latitude6/57.2957795130823)*COS(Client.Latitude/57.2957795130823)*
>>		COS(Client.Longitude/57.2957795130823-@Longitude4/57.2957795130823)>1
>>		THEN 1
>>		ELSE SIN(@Latitude7/57.2957795130823)*SIN(Client.Latitude/57.2957795130823)+
>>		COS(@Latitude8/57.2957795130823)*COS(Client.Latitude/57.2957795130823)*
>>		COS(Client.Longitude/57.2957795130823-@Longitude5/57.2957795130823)
>> 		END) as Distance 
>>	) Result
>>
>>   where (Distance <= 250)
>>
>>

>
>This works, thanks
>
>I added FROM Client after as Distance.


By the way

You are using a constant 3958.75586574. I believe this is the radius of the earth in miles. If you want km, I'd use 6371

Source - http://www.movable-type.co.uk/scripts/latlong-db.html