SQL Server 2019

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create table test(
  date_column varchar(20)
)
insert into test(date_column)
values('20150812'),
('03/07/2013'),
('2017-09-23')
3 rows affected

select * from test

date_column

20150812

03/07/2013

2017-09-23

select convert(varchar(10),cast(date_column as date),112) from test

(No column name)

20150812

20130307

20170923