使用XQuery来提取XML数据

Question

考虑下面的XML的最佳方式：

<Persons num="3"> 
    <Person age="5" /> 
    <Person age="19" /> 
</Persons> 

有必要提取该XML到关系表：

Persons table (Age1 int, Age2 int, Age3 int , Age4 int) 

解析必须满足以下约束条件：

• 所有年龄大于等于18岁的人都必须分配到列号最小的列，值必须是18
• 如果不给的人的年龄就等于18
• 随着年龄的所有人< 18必须遵循
• 如果有少于4人，那些不提供必须有年龄= -1

在给定的例子中，有3人，其中2人的年龄分别为5人和19人。表格人员的内容必须如下：

18 18 5 -1 

是否有最佳方式使用xpath？

到目前为止我可以解析XML和指定年龄，但有什么不清楚的是如何使排序：

declare @XmlData xml = 
'<Persons num="3"> 
    <Person age="5" /> 
    <Person age="19" /> 
</Persons>' 

declare @Persons table (Age1 int, Age2 int, Age3 int , Age4 int) 
insert into @Persons (Age1, Age2, Age3, Age4) 
select ISNULL(Age1, case when Num>= 1 then 18 else -1 end) Age1 
    , ISNULL(Age2, case when Num>= 2 then 18 else -1 end) Age2 
    , ISNULL(Age3, case when Num>= 3 then 18 else -1 end) Age3 
    , ISNULL(Age4, case when Num>= 4 then 18 else -1 end) Age4 
from (
    select Persons.Person.value('@num','smallint') as Num 
      ,Persons.Person.value('Person[@age<18][1]/@age','smallint') as Age1 
      ,Persons.Person.value('Person[@age<18][2]/@age','smallint') as Age2 
      ,Persons.Person.value('Person[@age<18][3]/@age','smallint') as Age3 
      ,Persons.Person.value('Person[@age<18][4]/@age','smallint') as Age4 
    from @XmlData.nodes('/Persons') Persons(Person) 
) Persons 

select * 
from @Persons 

结果是

5 18 18 -1 

Answer 1

另一种解决方案需要一点点更多的sql代码，但估计执行计划的成本只有~80。

有一个约束WRT问题陈述：人/ @ NUM已经等于了一些人标签

限制是：

• 限制每间房的人数

下面是SQL代码：

--//initial xml data 
declare @XmlData xml = 
'<Persons roomid="1" num="3"> 
    <Person age="19" /> 
    <Person age="10" /> 
    <Person age="5" /> 
</Persons> 
<Persons roomid="4" num="4"> 
    <Person age="17" /> 
    <Person age="10" /> 
    <Person age="5" /> 
    <Person age="1" /> 
</Persons>' 

--//shade xml into temporal table: rank is applied to an age in descreasing order 
declare @tmp table (age int, roomid int, orderid int) 
insert into @tmp(age,roomid,orderid) 
select Persons.age 
     ,Persons.roomid 
     ,ROW_NUMBER() over (partition by Persons.roomid order by Persons.age desc) 
from(
    select Ps.P.value('(@age)[1]','smallint') age  
      ,Ps.P.value('(../@roomid)[1]','smallint') roomid 
    from @XmlData.nodes('/Persons/Person') Ps(P) 
)Persons 
order by Persons.roomid,Persons.age desc  

--//provide ordering for roomid: since roomid may be different (the only thing that is required that roomid is unique) 
declare @roomidmapping table (roomid int, roomorderid int) 
insert into @roomidmapping(roomid, roomorderid) 
select roomid, ROW_NUMBER() over (order by roomid asc) 
from @tmp 
group by roomid 
declare @roomnumber int = @@ROWCOUNT 
--//final result 
;WITH ConsequtiveNums AS 
(
    SELECT 1 AS Number 
    UNION ALL 
    SELECT Number+1 
    FROM ConsequtiveNums 
    WHERE Number<@roomnumber 
) 
select (select case when age>18 then 18 else age end from @tmp T inner join @roomidmapping M on T.roomid = M.roomid where T.orderid = 1 and M.roomorderid = CN.Number) 
     ,(select case when age>18 then 18 else age end from @tmp T inner join @roomidmapping M on T.roomid = M.roomid where T.orderid = 2 and M.roomorderid = CN.Number) 
     ,(select case when age>18 then 18 else age end from @tmp T inner join @roomidmapping M on T.roomid = M.roomid where T.orderid = 3 and M.roomorderid = CN.Number) 
     ,(select case when age>18 then 18 else age end from @tmp T inner join @roomidmapping M on T.roomid = M.roomid where T.orderid = 4 and M.roomorderid = CN.Number) 
from ConsequtiveNums CN 

Answer 2

我发现有点脏的解决方案：

select ISNULL(Age1, case when Num>= 1 then 18 else -1 end) Age1 
    , ISNULL(Age2, case when Num>= 2 then 18 else -1 end) Age2 
    , ISNULL(Age3, case when Num>= 3 then 18 else -1 end) Age3 
    , ISNULL(Age4, case when Num>= 4 then 18 else -1 end) Age4 
from (
    select Persons.Person.value('@num','smallint') as Num 
      ,Persons.Person.value('xs:integer(fn:number(@num))+1','int') as Num1 
      ,Persons.Person.value('Person[@age<18][xs:integer(fn:number(../@num))][1]/@age','smallint') as Age1 
      ,Persons.Person.value('Person[@age<18][xs:integer(fn:number(../@num))-1][1]/@age','smallint') as Age2 
      ,Persons.Person.value('Person[@age<18][xs:integer(fn:number(../@num))-2][1]/@age','smallint') as Age3 
      ,Persons.Person.value('Person[@age<18][xs:integer(fn:number(../@num))-3][1]/@age','smallint') as Age4 
    from @XmlData.nodes('/Persons') Persons(Person) 
) Persons 

解决方案的想法是首先提取那些> = 18的联系人，然后提取那些是0 <年龄< 18最后定那些不提供给-1

UPD：尽管该解决方案提供了正确的结果，它的成本是很高的事实：〜1000估计的执行计划