SQL Server - Actualizar Data desde una consulta.

DECLARE @Codigos as table (Codigo varchar(20))

INSERT INTO @Codigos VALUES

('34639053'),

('34639053'),

('59023576'),

('59023576'),

('84520777'),

('84520777'),

('84520777')

SELECT Codigo, count(Codigo) as Registrados

from @Codigos

group by Codigo

CREATE TABLE Codigos(

    Codigo varchar(20) NULL,

    REGISTROS int

);

INSERT INTO Codigos VALUES ('34639053',0),

('34639053',0),

('59023576',0),

('59023576',0),

('84520777',0),

('84520777',0),

('84520777',0)

select * from Codigos

SELECT Codigo, count(Codigo) as Registrados

from Codigos

group by Codigo

update Codigos

set REGISTROS=B.Registrados

from codigos A inner join (

SELECT Codigo, count(Codigo) as Registrados

from Codigos

group by Codigo) as B

on a.Codigo=B.Codigo

select * from Codigos

drop table Codigos