Why query does not fail with nonexistent column in subquery?

Question

I misspelled in my query and faced with MySQL\'s strange behaviour.

create table aaa (id bigint auto_increment primary key, 
                  amount int not nul         


        

Answer 1

This query:

select sum(amount)
from aaa
where id not in (select id from bbb);

Is interpreted as:

select sum(aaa.amount)
from aaa
where aaa.id not in (select aaa.id from bbb);

because bbb.id does not exist. When writing SQL, I suggest that you always use table aliases. The query that you thought you were writing:

select sum(aaa.amount)
from aaa
where aaa.id not in (select bbb.id from bbb);

would generate the error you expect.