如何从oracle生成xml

我有两张桌子如下

餐桌上的学生

表标记

mark_id     person_id   subject   marks
1           1           English    50
2           1           Maths      75

下面的查询给出如下所示的xml

select XMLElement(      "Students" ,
              (select XMLAgg( XMLElement("Student" ,                      
                             XmlElement( "Student_id","id")  ,
                             XmlElement(  "First_Name","firstname")  
                             ))
                             FROM students  )
                             )
                               AS "RESULT" 
From dual

<Students>
<Student>
<Student_id>1</Student_id>
<First_Name>John</First_Name>
</Student>
<Student>
<Student_id>2</Student_id>
<First_Name>Mike</First_Name>
</Student>
<Students>

如何实现如果我编写select查询，它将为第一个学生返回两行，因为它在第二个标记表中有两行要连接

select XMLElement(
         "Students" ,
         XMLAgg(
           XMLElement(
             "Student" ,
             XMLFOREST(
               s."Student_id" AS "id",
               s."First_Name" AS "firstname"
             ),
             m.marks
           )
         )
       )
FROM   students s
       LEFT OUTER JOIN
       ( SELECT person_id,
                XMLELEMENT(
                  "Marks",
                  XMLAGG(
                    XMLFOREST(
                      "subject",
                      "marks" AS "mark"
                    )
                  )
                ) AS marks
         FROM   Marks
       ) m
       ON ( s."PersonID" = m.person_id )

---

注：除非有特定的业务需求，否则为：；只需在任何地方使用不带引号的标识符，并让oracle管理不区分大小写。

取决于需求。如果有多个标记，并且每个学生只能有一行，则可以使用group by子句。@AluanHaddad可以有多个主题和标记供学生使用，有时没有标记。所以我使用左连接学生作为学生左连接标记作为。。。。分组方式。。。

<Students>
    <Student>
    <Student_id>1</Student_id>
    <First_Name>John</First_Name>
    <Marks>
     <subject>English</subject>
     <mark>50</mark>
     <subject>Maths</subject>
     <mark>75</mark>
    </Marks>
    </Student>
    <Student>
    <Student_id>2</Student_id>
    <First_Name>Mike</First_Name>
    <Marks/>
    </Student>
    <Students>

select XMLElement(
         "Students" ,
         XMLAgg(
           XMLElement(
             "Student" ,
             XMLFOREST(
               s."Student_id" AS "id",
               s."First_Name" AS "firstname"
             ),
             m.marks
           )
         )
       )
FROM   students s
       LEFT OUTER JOIN
       ( SELECT person_id,
                XMLELEMENT(
                  "Marks",
                  XMLAGG(
                    XMLFOREST(
                      "subject",
                      "marks" AS "mark"
                    )
                  )
                ) AS marks
         FROM   Marks
       ) m
       ON ( s."PersonID" = m.person_id )