使用xquery从xml中提取数据的最佳方法

Question

考虑以下 xml：

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

需要将此 xml 提取到关系表中：

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

解析必须满足以下约束：

• 所有年龄 >=18 的人必须分配到列号最小的列，并且该值必须为 18
• 如果未给出该人的年龄，则等于 18
• 所有年龄 <18 岁的人都必须遵循
• 如果少于 4 人，则未提供的人必须年龄=-1

在给定的示例中，有 3人，提供其中 2 人的年龄：分别为 5 岁和 19 岁。 Persons 表的内容必须如下所示：

18 18 5 -1

是否有使用 xpath 执行此操作的最佳方法？

到目前为止，我可以解析 xml 并分配年龄，但不清楚的是如何进行排序：

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更多的 sql 代码，但预计执行计划的成本仅为 80 左右。

问题陈述有一个约束：Persons/@num必须等于许多Person标签

限制是：

• 每个房间的人数有限

这是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

我发现了一个有点肮脏的解决方案：

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0<=18的联系人。年龄< 18 最后将未提供的设置为 -1

UPD：尽管解决方案提供了正确的结果，但其成本很高：估计执行计划中约为 1000