Question

我在Oracle-12c中有一个类似于accounts，posts，comments的典型论坛的模式。我正在编写一个查询来获取...

一位用户
所有该用户的帖子
对每个帖子的评论
和每条评论的作者。

查询如下所示：

select "accounts".*, "p".*, "c".*, "author".*
from "accounts"
cross apply (
    select * from "posts"
    where "posts"."author_id" = "accounts"."id"
) "p"
cross apply (
    select * from "comments"
    where "comments"."post_id" = "p"."id"
) "c"
left join "accounts" "author" on "author"."id" = "c"."author_id"
where "accounts"."id" = 1

此查询按预期工作。我正在使用CROSS APPLY而不是典型的JOIN，因为我将稍后添加OFFSET和FETCH以进行分页上。但是，问题是CROSS APPLY省略了没有评论的帖子，这是我不想要的。我希望保持结果中的帖子，即使他们没有评论。

所以我尝试将CROSS APPLY更改为OUTER APPLY。

select "accounts".*, "p".*, "c".*, "author".*
from "accounts"
outer apply (
    select * from "posts"
    where "posts"."author_id" = "accounts"."id"
) "p"
outer apply (
    select * from "comments"
    where "comments"."post_id" = "p"."id"
) "c"
left join "accounts" "author" on "author"."id" = "c"."author_id"
where "accounts"."id" = 1

但现在我收到了这个错误：

ORA-00904: "p"."id": invalid identifier
00904. 00000 -  "%s: invalid identifier"
*Cause:    
*Action:
Error at Line: 9 Column: 34

出于某种原因，我的第二个OUTER APPLY加入是抱怨我从第一个结果中引用"p"."id"。但是当我使用CROSS APPLY时它很好。

发生了什么事？为什么这些行为之间存在这种差异？

编辑：OUTER APPLY在这个基本示例中似乎没有必要。这是从一个更复杂的场景中提炼出来的，我必须坚持认为OUTER APPLY确实是必要的，但是这个场景的细节与我所问的实际问题无关 - 这是关于这种看似无证的行为差异在CROSS和OUTER APPLY之间。

编辑：

Oracle版本：数据库12c标准版12.1.0.2.0版 - 64位生产

客户端： Oracle SQL Developer版本4.2.0.16.356

服务器：uname -a - Linux ubuntu-1gb-sfo2-01 4.4.0-64-generic #85-Ubuntu SMP Mon Feb 20 11:50:30 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

DDL： link

Answer 1

要CodeFuller's回答，我只想补充一点（A）有一个可用于此bug的补丁和（B）有一个可在12.1.0.2中运行的解决方法，但我不知道它是否符合您的目的。

解决方法是基本嵌套连接，如下所示：

SELECT accounts.*,
       p.*,
       author.*
FROM   accounts
       CROSS APPLY (SELECT posts.id,
                           posts.author_id,
                           posts.text,
                           comments.comment_author_id,
                           comments.comment_text
                    FROM   posts
                           OUTER APPLY (SELECT comments.author_id comment_author_id,
                                               comments.text comment_text
                                        FROM   comments
                                        WHERE  comments.post_id = posts.id) comments
                    WHERE  posts.author_id = accounts.id) p
       LEFT JOIN accounts author
         ON author.id = p.comment_author_id
WHERE  accounts.id = 1;


ID   NAME      ID_1 AUTHOR_ID TEXT                                              COMMENT_AUTHOR_ID COMMENT_TEXT                            ID_2  NAME_1                               
---- --------- ---- --------- ------------------------------------------------- ----------------- --------------------------------------- ----- ------------------- 
   1 Fred         1         1 Fred wrote this and it has comments                               3 This is Helen's comment on Fred's post      3 Helen                                
   1 Fred         2         1 Fred wrote this and it does not have any comments
-------- End of Data --------
2 row(s) fetched

参考：用于解决方法的表DDL

CREATE TABLE accounts
(
  id     NUMBER PRIMARY KEY,
  name   VARCHAR2 (30)
);

CREATE TABLE posts
(
  id          NUMBER PRIMARY KEY,
  author_id   NUMBER,
  text        VARCHAR2 (240)
);

CREATE TABLE comments
(
  id          NUMBER PRIMARY KEY,
  post_id     NUMBER,
  author_id   NUMBER,
  text        VARCHAR2 (240)
);

INSERT INTO accounts (id, name)
VALUES (1, 'Fred');

INSERT INTO accounts (id, name)
VALUES (2, 'Mary');

INSERT INTO accounts (id, name)
VALUES (3, 'Helen');

INSERT INTO accounts (id, name)
VALUES (4, 'Iqbal');

INSERT INTO posts (id, author_id, text)
VALUES (1, 1, 'Fred wrote this and it has comments');

INSERT INTO posts (id, author_id, text)
VALUES (2, 1, 'Fred wrote this and it does not have any comments');

INSERT INTO posts (id, author_id, text)
VALUES (3, 4, 'Iqbal wrote this and it does not have any comments');

INSERT INTO comments (id,
                      post_id,
                      author_id,
                      text)
VALUES (1,
        1,
        3,
        'This is Helen''s comment on Fred''s post');

Answer 2

您的查询没有任何问题。您遇到了错误20356733/21547130，这是在12.1.0.2中引入的，如here所述。为了克服它，请使用12.1.0.2之前的版本或应用最新更新（修复的链接线程声明在12.1.0.2.160419补丁集更新中可用）。

此答案主要由Matthew McPeak和Martin Smith找到。我刚刚按照下面的描述进行了首次尝试，发现该问题在Oracle 12.1.0.1上无法重现。

第一次回答尝试：

我已经使用您的架构创建了测试数据库，这两个查询对我来说都很好。第一个不返回没有评论的帖子，第二个返回所有帐户帖子，没有任何ORA-00904错误。我在Oracle 12c上做过这个测试。

继续提问：

尝试从帖子中复制/粘贴并执行第二个查询。有时候一些令人讨厌的错别字会潜入查询中。来自您帖子的确切查询可以按预期为我工作。
如果您仍然遇到同样的错误，请提供您用于创建accounts，posts和comments表格的DDL。
请指定您正在使用的SQL客户端。错误肯定是在服务器端，但在这种奇怪的情况下，每一个细节都可以产生影响。

我的测试数据库：

CREATE TABLE "accounts"
(
    "id" NUMBER(11) NOT NULL,
    "name" NVARCHAR2(256),
    CONSTRAINT ACCOUNTS_PK PRIMARY KEY ("id")
)
/

CREATE TABLE "posts"
(
    "id" NUMBER(11) NOT NULL,
    "author_id" NUMBER(11) NOT NULL,
    "post_text" NVARCHAR2(1024),
    CONSTRAINT POSTS_PK PRIMARY KEY ("id"),
    CONSTRAINT POST_ACCOUNT_FK FOREIGN KEY ("author_id") REFERENCES "accounts" ("id") ON DELETE CASCADE
)
/

CREATE TABLE "comments"
(
    "id" NUMBER(11) NOT NULL,
    "author_id" NUMBER(11) NOT NULL,
    "post_id" NUMBER(11) NOT NULL,
    "comment_text" NVARCHAR2(1024),
    CONSTRAINT COMMENTS_PK PRIMARY KEY ("id"),
    CONSTRAINT COMMENT_ACCOUNT_FK FOREIGN KEY ("author_id") REFERENCES "accounts" ("id") ON DELETE CASCADE,
    CONSTRAINT COMMENT_POST_FK FOREIGN KEY  ("post_id") REFERENCES "posts" ("id") ON DELETE CASCADE
)
/

INSERT INTO "accounts"("id", "name") VALUES(1, 'testuser')
/
INSERT INTO "posts"("id", "author_id", "post_text") VALUES(1, 1, 'First test post')
/
INSERT INTO "posts"("id", "author_id", "post_text") VALUES(2, 1, 'Second test post')
/
INSERT INTO "comments"("id", "author_id", "post_id", "comment_text") VALUES(1, 1, 2, 'It is a very cool post')
/
COMMIT

“CROSS APPLY”和“OUTER APPLY”

2 个答案:

参考：用于解决方法的表DDL