Oracle第二层子查询居然不认最外层表中的列,在某些版本中一直存在.

至少我公司版本10.2.0.3还有这个问题,ANSI SQL的问题.转自Asktom，原帖链接.

http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:1853075500346799932

You Asked

create table con ( content_id number);
create table mat ( material_id number, content_id number, resolution number, 
file_location varchar2(50));
create table con_groups (content_group_id number, content_id number);

insert into con values (99);
insert into mat values (1, 99, 7, 'C:\foo.jpg');
insert into mat values (2, 99, 2, '\\server\xyz.mov');
insert into mat values (3, 99, 5, '\\server2\xyz.wav');
insert into con values (100);
insert into mat values (4, 100, 5, 'C:\bar.png');
insert into mat values (5, 100, 3, '\\server\xyz.mov');
insert into mat values (6, 100, 7, '\\server2\xyz.wav');
      
insert into con_groups values (10, 99);
insert into con_groups values (10, 100);

commit;

SELECT m.material_id,
       (SELECT file_location 
          FROM (SELECT file_location
                  FROM mat
                 WHERE mat.content_id = m.content_id
              ORDER BY resolution DESC) special_mats_for_this_content            
         WHERE rownum = 1) special_mat_file_location                                     
  FROM mat m
 WHERE m.material_id IN (select material_id 
                           from mat
                     inner join con on con.content_id = mat.content_id
                     inner join con_groups on con_groups.content_id = con.content_id
                          where con_groups.content_group_id = 10);

Please consider the number 10 at the end of the query to be a parameter. In other words this value is just hardcoded in this example; it would change depending on the input.

My question is: Why do I get the error

"M"."CONTENT_ID": invalid identifier 

for the nested, correlated subquery? Is there some sort of nesting limit? This subquery needs to be ran for every row in the resultset because the results will change based on the content_id, which can be different for each row. How can I accomplish this with Oracle?

Not that I'm trying to start a SQL Server vs Oracle discussion, but I come from a SQL Server background and I'd like to point out that the following, equivalent query runs fine on SQL Server:

create table con ( content_id int);
create table mat ( material_id int, content_id int, resolution int, file_location 
varchar(50));
create table con_groups (content_group_id int, content_id int);

insert into con values (99);
insert into mat values (1, 99, 7, 'C:\foo.jpg');
insert into mat values (2, 99, 2, '\\server\xyz.mov');
insert into mat values (3, 99, 5, '\\server2\xyz.wav');
insert into con values (100);
insert into mat values (4, 100, 5, 'C:\bar.png');
insert into mat values (5, 100, 3, '\\server\xyz.mov');
insert into mat values (6, 100, 7, '\\server2\xyz.wav');
      
insert into con_groups values (10, 99);
insert into con_groups values (10, 100);

SELECT m.material_id,
       (SELECT file_location 
          FROM (SELECT TOP 1 file_location
                  FROM mat
                 WHERE mat.content_id = m.content_id
              ORDER BY resolution DESC) special_mats_for_this_content            
               ) special_mat_file_location                                     
  FROM mat m
 WHERE m.material_id IN (select material_id 
                           from mat
                     inner join con on con.content_id = mat.content_id
                     inner join con_groups on con_groups.content_id = con.content_id
                          where con_groups.content_group_id = 10);

Can you please help me understand why I can do this in SQL Server but not Oracle?

Thanks,
Nate

and we said...

ANSI SQL has table references (correlation names) scoped to just one level deep

ops$tkyte%ORA10GR2> select (select count(*) from (select * from scott.emp where ename = 
dual.dummy)) from dual;
select (select count(*) from (select * from scott.emp where ename = dual.dummy)) from 
dual
                                                                    *
ERROR at line 1:
ORA-00904: "DUAL"."DUMMY": invalid identifier



ops$tkyte%ORA10GR2> select (select count(*) from scott.emp where ename = dual.dummy) from 
dual;

(SELECTCOUNT(*)FROMSCOTT.EMPWHEREENAME=DUAL.DUMMY)
--------------------------------------------------
                                                 0

the first one fails because we tried to push the dual.dummy reference two levels down - in correlated subqueries, they only go a level.

ops$tkyte%ORA10GR2> SELECT m.material_id, m.content_id,
  2            (SELECT max(file_location) keep (dense_rank first order by resolution 
desc)
  3               FROM mat
  4              WHERE mat.content_id = m.content_id) special_mat_file_location
  5    FROM mat m
  6   WHERE m.material_id IN (select material_id
  7                             from mat
  8                       inner join con on con.content_id = mat.content_id
  9                       inner join con_groups on con_groups.content_id = con.content_id
 10                            where con_groups.content_group_id = 10);

MATERIAL_ID CONTENT_ID SPECIAL_MAT_FILE_LOCATION
----------- ---------- --------------------------------------------------
          1         99 C:\foo.jpg
          2         99 C:\foo.jpg
          3         99 C:\foo.jpg
          4        100 \\server2\xyz.wav
          5        100 \\server2\xyz.wav
          6        100 \\server2\xyz.wav

6 rows selected.