我有一张有事故的大桌子。有了这个，我想附加事件附件和事件注释中的值。我使用了左外连接，因为事件可能有也可能没有任何意见或附件 现在当我使用多个外连接时，我得到重复的行。
所有表格都有一个commonID值
INC1 ATT1 COMMENT1
INC1 ATT1 COMMENT2
INC1 ATT2 COMMENT1
INC1 ATT2 COMMENT2
但实际上输出应该是：
INC1 ATT1 COMMENT1
INC1 ATT2 COMMENT2
以便在将自己附加到事件表时附件和注释值是独立的。
select inc,att.attname,comment.commenttext
from inc
left outer join att inc.incidentID=att.incidentID
left outer join comment inc.incidentID=comment .incidentID
这可能吗？
答案 0 :(得分：2)
到目前为止，我从你的回答中得到的一点是，对于某一特定事件，其附件与其评论之间没有直接关系。 如果我理解正确，您希望将事件视为附件和注释的简单“容器”，并且您只需要列出每个事件。哪一个 附件恰好出现在同一行中，因为特定评论是偶然发生的。
测试数据：
SQL> CREATE TABLE inc (incidentid NUMBER, incname VARCHAR2(20));
Table created.
SQL> INSERT INTO inc VALUES (1,'incident 1');
1 row created.
SQL> INSERT INTO inc VALUES (2,'incident 2');
1 row created.
SQL> CREATE TABLE att (att_id NUMBER, incidentid NUMBER, attname VARCHAR2(20));
Table created.
SQL> INSERT INTO att VALUES (101, 1, 'attachment 1');
1 row created.
SQL> INSERT INTO att VALUES (102, 1, 'attachment 2');
1 row created.
SQL> INSERT INTO att VALUES (103, 1, 'attachment 3');
1 row created.
SQL> INSERT INTO att VALUES (104, 1, 'attachment 4');
1 row created.
SQL> INSERT INTO att VALUES (105, 1, 'attachment 5');
1 row created.
SQL> INSERT INTO att VALUES (110, 2, 'attachment A');
1 row created.
SQL> INSERT INTO att VALUES (111, 2, 'attachment B');
1 row created.
SQL> INSERT INTO att VALUES (112, 2, 'attachment C');
1 row created.
SQL> CREATE TABLE comments (comment_id NUMBER, incidentid NUMBER, commenttext VARCHAR2(20));
Table created.
SQL> INSERT INTO comments VALUES (201, 1, 'first comment');
1 row created.
SQL> INSERT INTO comments VALUES (202, 1, 'second comment');
1 row created.
SQL> INSERT INTO comments VALUES (203, 1, 'third comment');
1 row created.
建议查询：
SQL> WITH a AS (
2 SELECT att.incidentid
3 , COUNT(att.att_id) rows_per_incident
4 FROM att
5 GROUP BY att.incidentid
6 UNION ALL
7 SELECT comments.incidentid
8 , COUNT(comments.comment_id) rows_per_incident
9 FROM comments
10 GROUP BY comments.incidentid
11 )
12 , b AS (
13 SELECT inc.incidentid
14 , inc.incname
15 , ROW_NUMBER()
16 OVER (PARTITION BY inc.incidentid ORDER BY NULL) row_num
17 FROM inc
18 , (SELECT ROWNUM multiplier FROM DUAL CONNECT BY LEVEL <= (SELECT MAX(rows_per_incident) FROM a))
19 )
20 , c AS (
21 SELECT att.att_id
22 , att.incidentid
23 , att.attname
24 , ROW_NUMBER()
25 OVER (PARTITION BY att.incidentid ORDER BY att.att_id) att_rn
26 FROM att
27 )
28 , d AS (
29 SELECT comments.comment_id
30 , comments.incidentid
31 , comments.commenttext
32 , ROW_NUMBER()
33 OVER (PARTITION BY comments.incidentid ORDER BY comments.comment_id) comm_rn
34 FROM comments
35 )
36 , e AS (
37 SELECT c.incidentid
38 , c.att_id
39 , c.attname
40 , c.att_rn rn
41 , d.comment_id
42 , d.commenttext
43 FROM c
44 , d
45 WHERE c.incidentid = d.incidentid (+)
46 AND c.att_rn = d.comm_rn (+)
47 UNION ALL
48 SELECT TO_NUMBER(NULL) incidentid
49 , TO_NUMBER(NULL) att_id
50 , NULL attname
51 , d.comm_rn rn
52 , d.comment_id
53 , d.commenttext
54 FROM d
55 WHERE NOT EXISTS (SELECT NULL
56 FROM c
57 WHERE c.incidentid = d.incidentid
58 AND c.att_rn = d.comm_rn)
59 )
60 , f AS (
61 SELECT b.incidentid
62 , b.incname
63 , b.row_num
64 , e.att_id
65 , e.attname
66 , e.comment_id
67 , e.commenttext
68 FROM b
69 LEFT OUTER JOIN e ON b.incidentid = e.incidentid
70 AND b.row_num = e.rn
71 )
72 SELECT f.incidentid
73 , f.incname
74 , f.att_id
75 , f.attname
76 , f.comment_id
77 , f.commenttext
78 FROM f
79 WHERE NOT (f.att_id IS NULL AND f.comment_id IS NULL)
80 ORDER BY f.incidentid
81 , f.row_num
82 ;
INCIDENTID INCNAME ATT_ID ATTNAME COMMENT_ID COMMENTTEXT
---------- -------------------- ---------- -------------------- ---------- --------------------
1 incident 1 101 attachment 1 201 first comment
1 incident 1 102 attachment 2 202 second comment
1 incident 1 103 attachment 3 203 third comment
1 incident 1 104 attachment 4
1 incident 1 105 attachment 5
2 incident 2 110 attachment A
2 incident 2 111 attachment B
2 incident 2 112 attachment C
8 rows selected.
SQL>