Logic for two tables mismatched columns

create table staging (clientid int primary key,addressdetails varchar(250));
insert into staging
select 100,'hyderbad,india' union all
select 101,'banglore,india' union all
select 102,'banglore,india'

create table oltp (client_id int primary key,address_details varchar(250));
insert into oltp
select 104,'newyork,usa' union all
select 105,'chicago,usa' union all
select 106,'washington,usa'

select * from oltp where client_id in (select client_id from staging)
o/p:
It returns all 2nd table rows.. instead of raising error that column-name is not existing in table

It will fetch all the values from outer query as inner query referring the same column from outer query .If a column is referenced in a subquery that does not exist in the table referenced by the subquery's FROM clause, but exists in a table referenced by the outer query's FROM clause, the query executes without error. SQL Server implicitly qualifies the column in the subquery with the table name in the outer query.