SQL - Contar registros con valor único

CREATE TABLE juguetes

	(

     ninio varchar(25),

     juguete varchar(25)

    );

INSERT INTO juguetes

(ninio, juguete)

VALUES

('fernando','patines'),

('david','patines'),

('david','canicas'),

('antonio','patines'),

('pedro', 'canicas')

;

select count(distinct ninio)

from   (

        select ninio

             , count(distinct juguete) cantidad

             , sum(case when juguete = 'patines' then 1 else 0 end) patines

        from   juguetes

        group  by ninio) as A

where   cantidad = 1

and     patines > 0

;

select ninio

     , count(distinct juguete) cantidad

     , sum(case when juguete = 'patines' then 1 else 0 end) patines

from   juguetes

group  by ninio;