Regarding subquery, surprizing thing.!

Question

Hello Gurus,
While writing quires for my application I did a typo, which made me realise below thing
Select column1, column2, column3
from table1
where column1 in (select column1 from table2) Above query works without producing error returning ALL rows from table1.
But the thing is Table2 dont have a column called 'column1' !!!
When I execute the inner query separately it gives 'Invalid Identifier' error, which is much obvious.
i.e.
select column1 from table2gives 'Invalid Identifier' error.
Then I am wondering how it works if its in subquery?

Answer 1

It works because column1 is a valid column in table1 and it is valid to reference a column in the outer table in your subquery. Obviously, in this case, it is an error, but it is necessary if you want to do something like a correlated subquery.
Your query is equivalent to
Select column1, column2, column3
from table1
where column1 in (select table1.column1 from table2)Justin