我的架构中有几个多对多的关系。例如,一个包有许多任务组,而任务组又有许多任务。所有表通过多对多表链接在一起,例如拥有包的主键和任务组的主键。 (我知道这并不是严格要求的,因为XML是一对多的,但是我想不到更好的结构)。
是否可以将查询结果作为XML反射(reflect)出一对多的结构?因此,结果应如下所示:
<package id=1>
<taskgroup id=1>
<task id=1>
<task id=2>
</taskgroup>
<taskgroup id=2>
<task id=3>
</taskgroup>
</package>
通过使用
XMLELEMENT()
和XMLATTRIBUTE()
函数来获取所有任务,我已经设法获得了想要的一部分。像这样: SELECT XMLELEMENT(name task,
XMLATTRIBUTES(p.name as packageName),
XMLELEMENT(name description, t.description),
XMLELEMENT(name tutorial,
XMLELEMENT(name someTaskChild1, t.data1)),
XMLELEMENT(name objectives,
XMLELEMENT(name someTaskChild2, t.data2)),
)
FROM packages p
INNER JOIN package_taskgroup pt ON p.id = pt.package_id
INNER JOIN taskgroups tg on pt.taskgroup_id = tg.id
INNER JOIN taskgroup_task tt on tg.id = tt.taskgroup_id
INNER JOIN tasks t on tt.task_id = t.id
WHERE p.id = somePackageId AND tg.id = someTaskGroupId
问题是如何将这些任务分为其父表元素?
最佳答案
尝试:
SELECT p.id as pack_id,
XMLELEMENT(name taskgroup,
XMLATTRIBUTES(tg.id as id),
XMLAGG(XMLELEMENT(name task,
XMLATTRIBUTES(t.id as id)) as xml_task_group
FROM packages p
JOIN package_taskgroup pt ON p.id = pt.package_id
JOIN taskgroups tg on pt.taskgroup_id = tg.id
JOIN taskgroup_task tt on tg.id = tt.taskgroup_id
JOIN tasks t on tt.task_id = t.id
WHERE p.id = somePackageId
GROUP BY p.id, tg.id
这将为您提供您指定的
p.id
的所有任务组。然后:
SELECT XMLELEMENT(name package,
XMLATTRIBUTES(pack_id as id),
XMLAGG(xml_task_group))
FROM (previous SELECT here)
这将为您提供您指定的结构。
详细信息:XMLAGG,XML functions
加入的select将如下所示:
SELECT XMLELEMENT(name package,
XMLATTRIBUTES(pack_id as id),
XMLAGG(xml_task_group))
FROM (SELECT p.id as pack_id,
XMLELEMENT(name taskgroup,
XMLATTRIBUTES(tg.id as id),
XMLAGG(XMLELEMENT(name task,
XMLATTRIBUTES(t.id as id)
))) as xml_task_group
FROM packages p
JOIN package_taskgroup pt ON p.id = pt.package_id
JOIN taskgroups tg on pt.taskgroup_id = tg.id
JOIN taskgroup_task tt on tg.id = tt.taskgroup_id
JOIN tasks t on tt.task_id = t.id
WHERE p.id = somePackageId
GROUP BY p.id, tg.id) t
GROUP BY pack_id
我只是将第一个选择复制到第二个选择的
FROM
子句中。