Oracle 11g - 使用m到n关系表连接多行数据

Question

我可能有一些简单的问题，但我仍然无法弄清楚如何让事情发挥作用。

我有三个包含这些重要字段的表格：

1. 规则 - RuleOID
2. RuleToModificationReason - RuleOID，MdfnReasonOID
3. ModificationReason - MdfnReasonOID，MdfnTyp（CREATION或DELETION），MdfnDetail

并且f.e。我有这些数据：

1. 规则 - RuleOID = 1
2. 的 RuleToModificationReason
   • RuleOID = 1，MdfnReasonOID = 1
   • RuleOID = 1，MdfnReasonOID = 2
3. 的 ModificationReason
   • MdfnReasonOID = 1，MdfnTyp ='CREATION'，MdfnDetail ='创作细节'
   • MdfnReasonOID = 2，MdfnTyp ='DELETION'，MdfnDetail ='删除详情'

我希望在一行上输出用于创建和删除规则oid。

f.e。 ：RuleOID，创建详细信息，删除详细信息。

我可以将它加载到两行中，如：

1. RuleOID，创建详细信息，NULL
2. RuleOID，NULL，删除详细信息。

创建和删除原因可以为null。

甚至可能吗？

Answer 1

如果您确定某个规则的大多数始终存在一个创建详细信息，并且大多数给定规则的一个删除详细信息，然后你可以使用子查询：

SELECT Rule.RuleOID,
       ( SELECT MdfnDetail
           FROM ModificationReason
          WHERE MdfnType = 'CREATION'
            AND MdfnReasonOID IN
                 ( SELECT MdfnReasonOID
                     FROM RuleToModificationReason
                    WHERE RuleOID = Rule.RuleOID
                 )
       ) AS CreationReason,
       ( SELECT MdfnDetail
           FROM ModificationReason
          WHERE MdfnType = 'DELETION'
            AND MdfnReasonOID IN
                 ( SELECT MdfnReasonOID
                     FROM RuleToModificationReason
                    WHERE RuleOID = Rule.RuleOID
                 )
       ) AS DeletionReason
  FROM Rule
;

（也可以用JOIN来实现这一点，但这样做会更加棘手。）

Answer 2

它会对你有用吗？

SELECT a.RuleOID, 
CASE
  WHEN b.MdfnTyp = 'CREATION' THEN b.MdfnDetail
  ELSE NULL -- can omit, case has default "else null"
END AS creation_detail,
CASE
  WHEN b.MdfnTyp = 'DELETION' THEN b.MdfnDetail
  ELSE NULL -- can omit, case has default "else null"
END AS deletion_detail

RuleToModificationReason a
INNER JOIN ModificationReason b ON (a.MdfnReasonOID = b.MdfnReasonOID)

注意：规则表已按目的跳过（假设参照完整性由约束强制执行），因为您不使用该表中的任何字段

Answer 3

select crtr.RuleOID RuleOID, crt.MdfnDetail Creation_detail, dlt.MdfnDetail Deletion_detail
from ModificationReason crt, ModificationReason dlt, RuleToModificationReason crtr, RuleToModificationReason dltr
where crt.MdfnTyp = 'CREATION' and dlt.MdfnTyp = 'DELETION'
and crt.MdfnReasonOID = crtr.MdfnReasonOID
and dlt.MdfnReasonOID = dltr.MdfnReasonOID
and crtr.RuleOID = dltr.RuleOID   

（无法检查）