oracle10g - sql not throwing invalid identifier -

i asking question because not getting error expect there should error. please me understand under circumstances possible. have query:

select foracid,acct_name, schm_code, schm_type tbaadm.gam  acid  in(select acid tbaadm.iar); 

this query returning results without throwing error. expect invalid identifier because table tbaadm.iar not have field acid. when run:

 select acid tbaadm.iar; 

i get:

ora-00904: "acid": invalid identifier 00904. 00000 -  "%s: invalid identifier" *cause:     *action: error @ line: 772 column: 8 

i using sqldeveloper , oracle 10g. kind of strange me. worth mention though there field in tbaadm.iar id , right query should be:

select foracid,acct_name, schm_code, schm_type tbaadm.gam  acid  in(select entity_id tbaadm.iar); 

what going on here?

a subquery that's used in in clause can reference columns outer query, because necessary in correlated subqueries. clause equivalent to:

where acid in (select tbaadm.gam.acid tbaadm.iar) 

an example of correlated subquery shows why necessary is:

select * outer_table somefield = (select someotherfield                     inner_table                    inner_table.id = outer_table.inner_id) 

this more common use, field outer table used in where clause of subquery. sql isn't picky field outer query used. can used anywhere in subquery expression permitted, includes select clause.