SQL Server 2022

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create table sua_tabela(id int, codnome int, nome varchar(10), disc varchar(10), nota varchar(4), qtd int);
insert into sua_tabela(id, CodNome, Nome, Disc, Nota) values
(1,       123,               'A',         'MATE',      6),  
(2,       123,                'A',         'MATE',      7),        
(3,       123,                'A',        'PORT',      8),        
(4,       123,                'A',        'PORT',      9),        
(5,       345,                'M',        'MATE',      9),        
(6,       345,                'M',        'MATE',      8),        
(7,       345,                'M',        'MATE',      7),                  
(8,       345,                'M',        'PORT',      7),        
(9,       345,                'M',        'CIEN',       7)

SELECT t.id, t.CodNome, t.Nome, t.Disc, t.Nota, s.qtd
FROM sua_tabela t
JOIN (
  SELECT CodNome, Nome, Disc, COUNT(*) AS qtd
  FROM sua_tabela
  GROUP BY CodNome, Nome, Disc
) s
ON t.CodNome = s.CodNome AND t.Nome = s.Nome AND t.Disc = s.Disc
ORDER BY t.id;

id	CodNome	Nome	Disc	Nota	qtd
1	123	A	MATE	6	2
2	123	A	MATE	7	2
3	123	A	PORT	8	2
4	123	A	PORT	9	2
5	345	M	MATE	9	3
6	345	M	MATE	8	3
7	345	M	MATE	7	3
8	345	M	PORT	7	1
9	345	M	CIEN	7	1