在 Db2 (SQL/XML) 中使用 xmlquery 从 xml 中选择元素

Question

我在 Db2 中创建了这样的表：

create table xml_file(data xml not null)

这是 xml 的确切结构：

<?xml version="1.0" encoding="UTF-8" ?>
     <student id="20140021">
          <name>Tom</name>
          <surname>Johnson</surname>
          <birth_date>"05/11/1995"</birth_date>
          <birth_place>"Miami"</birth_place>
          <points>9.45</points>
     </student>

我想为所有姓名为 Ben 且出生地为芝加哥的学生提供 ID、姓名、姓氏和积分。

我写了这样的东西：

select xmlquery('$DATA/student/data(@id)') as ID,
       xmlquery('$DATA/student/name/text()') as NAME,
       xmlquery('$DATA/student/surname/text()') as SURNAME,
       xmlquery('$DATA/student/points/text()') as POINTS
from xml_file
where xmlexists('$DATA/student[birth_place = "Chicago"]')
and xmlexists('$DATA/student[name = "Ben"]');

我得到的只是这条消息： “FETCHED 0 RECORDS, 0 RECORDS SHOWN” （这是在 IBM Data Studio 中）。

有人能告诉我我做错了什么吗？

Answer 1

尝试这个：

/*
WITH xml_file (data) AS 
(
VALUES
XMLPARSE
(DOCUMENT '<?xml version="1.0" encoding="UTF-8" ?>
     <student id="20140021">
          <name>Tom</name>
          <surname>Johnson</surname>
          <birth_date>"05/11/1995"</birth_date>
          <birth_place>"Miami"</birth_place>
          <points>9.45</points>
     </student>'
)
)
*/
SELECT X.*
FROM 
  xml_file V
, XMLTABLE
  ('$doc/student' PASSING V.data AS "doc"
   COLUMNS
     ID      INT         PATH '@id'
   , NAME    VARCHAR(20) PATH 'name'
   , SURNAME VARCHAR(20) PATH 'surname'
   , POINTS  DEC(5, 2)   PATH 'points'
  ) X
WHERE XMLEXISTS('$doc/student[birth_place = """Miami""" and name = "Tom"]' PASSING V.data AS "doc");

Answer 2

尝试用一个替换你的两个where xmlexists （这与问题中的示例 xml 一起使用，而不是你的代码）：

where xmlexists('$DATA//student[birth_place/text()['Miami']][name/text()["Tom"]]');

或者，需要两个：

where xmlexists('$DATA/student[birth_place/text()['Miami']]')
and xmlexists('$DATA/student[name/text()["Tom"]]');

看看是否有效。

Answer 3

出生地元素包含导致 XPath 评估错误的双引号。 为避免这种情况，请将where xmlexists('$DATA/student[birth_place = "Chicago"]')替换为以下 XPath 表达式之一：

XPath 1.0 友好：

where xmlexists('$DATA/student/birth_place[substring(.,2,string-length(/student/birth_place)-2)="Chicago"]')

XPath 2.0 友好：

where xmlexists('$DATA/student/birth_place[translate(.,codepoints-to-string(34),"")="Chicago"]')

XPath 用于测试您的样本数据：

/student/birth_place[substring(.,2,string-length(/student/birth_place)-2)="Miami"]
/student/birth_place[translate(.,codepoints-to-string(34),"")="Miami"]