Unexpected results for DELETE FROM in SQL Server - sql-server

Question

Something rare its happens in my code.
Check this:
if object_id('inscriptos') is not null
drop table inscriptos;
if object_id('socios') is not null
drop table socios;
create table socios
(
numero int identity,
documento char(8),
nombre varchar(30),
domicilio varchar(30),
primary key (numero)
);
create table inscriptos
(
numerosocio int not null,
deporte varchar(20) not null,
matricula char(1),-- 'n' o 's'
primary key(numerosocio, deporte),
constraint FK_inscriptos_socio
foreign key (numerosocio) references socios(numero)
);
GO
insert into socios values('23333333', 'Alberto Paredes', 'Colon 111');
insert into socios values('24444444', 'Carlos Conte', 'Sarmiento 755');
insert into socios values('25555555', 'Fabian Fuentes', 'Caseros 987');
insert into socios values('26666666', 'Hector Lopez', 'Sucre 344');
insert into inscriptos values(1, 'tenis', 's');
insert into inscriptos values(1, 'basquet', 's');
insert into inscriptos values(1, 'natacion', 's');
insert into inscriptos values(2, 'tenis', 's');
insert into inscriptos values(2, 'natacion', 's');
insert into inscriptos values(2, 'basquet', 'n');
insert into inscriptos values(2, 'futbol', 'n');
insert into inscriptos values(3, 'tenis', 's');
insert into inscriptos values(3, 'basquet', 's');
insert into inscriptos values(3, 'natacion', 'n');
insert into inscriptos values(4, 'basquet', 'n');
And here comes the error that I don't understand, I must delete all the rows where in the field "registration" = "n", as you can see there are only 4 records where the value "n" appears in the field registration. But in the following query deletes 8 RECORDS instead of deleting 4 RECORDS.
CODE
DELETE FROM inscriptos
WHERE numerosocio IN (SELECT s.numero
FROM socios AS s
JOIN inscriptos AS i ON (i.numerosocio = s.numero)
WHERE i.matricula = 'n');
Do you know why this happens? I really can't understand it
THANKS!

Answer 1

Your inner SELECT returns this:
numero
------
2
2
3
4
And so your DELETE becomes
DELETE FROM inscriptos
WHERE numerosocio IN (2, 3, 4)
If you check what rows match that condition:
SELECT * FROM inscriptos
WHERE numerosocio IN (2, 3, 4)
you get this result - 8 rows - and those will be deleted:
numerosocio deporte matricula
-----------------------------------
2 basquet n
2 futbol n
2 natacion s
2 tenis s
3 basquet s
3 natacion n
3 tenis s
4 basquet n
So what exactly do you want to delete??
How about this:
DELETE FROM inscriptos
WHERE matricula = 'n'
This would delete those 4 rows with matricula = 'n' - why do you even need that subquery?!?!