在某些版本的Oracle中是否存在相关子查询的嵌套限制？

Question

以下代码将帮助您理解我的问题:

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);

请将查询末尾的数字10视为参数.换句话说,这个值在这个例子中只是硬编码; 它会根据输入而改变.

我的问题是:为什么我会收到错误

"M"."CONTENT_ID": invalid identifier 

对于嵌套的相关子查询？有某种嵌套限制吗？需要为结果集中的每一行运行此子查询,因为结果将根据content_id进行更改,而content_id对于每一行可能会有所不同.我如何用Oracle实现这一目标？

并不是说我正在尝试启动SQL Server与Oracle讨论,但我来自SQL Server后台,我想指出以下等效查询在SQL Server上正常运行:

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);

能否帮助我理解为什么我可以在SQL Server中执行此操作但不能在Oracle 9i中执行此操作？如果存在嵌套限制,如何在Oracle中的单个选择查询中完成此操作而不使用循环和/或临时表？

Answer 1

最新版本的Oracle没有限制,但大多数旧版本的Oracle都具有1深度的嵌套限制.

这适用于所有版本:

SELECT  (
        SELECT  *
        FROM    dual dn
        WHERE   dn.dummy = do.dummy
        )
FROM    dual do

此查询在12c和18c中有效,但在10g和11g中不起作用.(但是,至少有一个10g版本允许此查询.并且有一个补丁可以在11g中启用此行为.)

SELECT  (
        SELECT  *
        FROM    (
                SELECT  *
                FROM    dual dn
                WHERE   dn.dummy = do.dummy
                )
        WHERE   rownum = 1
        )
FROM    dual do

如果有必要,你可以使用窗口函数解决这个限制(你可以使用它SQL Server:)

SELECT  *
FROM    (
        SELECT  m.material_id, ROW_NUMBER() OVER (PARTITION BY content_id ORDER BY resolution DESC) AS rn
        FROM    mat m
        WHERE   m.material_id IN
                (
                SELECT  con.content_id
                FROM    con_groups
                JOIN    con
                ON      con.content_id = con_groups.content_id
                WHERE   con_groups.content_group_id = 10
                )
        )
WHERE   rn = 1