XML Oracle：识别现有但为空的元素

Question

我是使用 Oracle 的 xml DB 的新手，我开始了解它，但有一件重要的事情我无法做到：我需要确定 1.如果一个元素存在 2.如果是空的

不幸的是 XMLExists() 只是混合了两个答案。

我的查询的一小部分：

SELECT case when XMLEXISTS('/' passing by ref c3.CLASS) then 1 else 0 end E_CLASS,        
       c3.CLASS      
FROM XML_TEST x,
   XMLTABLE ('/Data/EMPLOYER'
                    PASSING x.File_XML
                    COLUMNS DOSSIER           NUMBER(8)       PATH     'DOSSIER',
                            SUMMARY           XMLTYPE         PATH 'SUMMARY'
            ) e,
   XMLTABLE ('/SUMMARY'
                PASSING e.SUMMARY
                COLUMNS BEGINDATE          DATE            PATH 'BEGINDATE',                            
                        WORKER             XMLTYPE         PATH 'WORKER'
            ) c1,
   XMLTABLE ('/WORKER'
                PASSING c1.WORKER
                COLUMNS NRWORKER           NUMBER(7)       PATH 'NRWORKER',                            
                        RESULT_DETAIL      XMLTYPE         PATH 'RESULT_DETAIL'
            ) c2 ,
    XMLTABLE ('/RESULT_DETAIL'
                PASSING c2.RESULT_DETAIL
                COLUMNS CODE               CHAR(5)         PATH 'CODE',                            
                        MINUTES            NUMBER(5)       PATH 'MINUTES',                            
                        CLASS              CHAR(1)         PATH 'CLASS'                            
            ) c3 ;

Answer 1

您可以使用//[not(text())][not(*)] 到find elements without any text and without children。

所以在你的上下文中你可以使用：

CASE
WHEN c2.RESULT_DETAIL IS NULL
     OR
     XMLEXISTS(
       '/RESULT_DETAIL/CLASS[not(text())][not(*)]'
       PASSING c2.RESULT_DETAIL
     )
THEN 1
ELSE 0
END AS isClassEmpty

你也可以LEFT OUTER JOIN你的表格，这样丢失的元素仍然会出现，然后你可以测试一下CLASS的值是否是NULL：

Oracle 设置：

CREATE TABLE XML_TEST ( File_XML ) AS
SELECT XMLTYPE( '<Data>
  <EMPLOYER>
    <DOSSIER>1</DOSSIER>
    <SUMMARY>
      <BEGINDATE>2019-02-13</BEGINDATE>
      <WORKER>
        <NRWORKER>42</NRWORKER>
        <RESULT_DETAIL>
          <CODE>12345</CODE>
          <MINUTES>0</MINUTES>
          <CLASS></CLASS>
        </RESULT_DETAIL>
      </WORKER>
    </SUMMARY>
  </EMPLOYER>
</Data>' ) FROM DUAL UNION ALL
SELECT XMLTYPE( '<Data>
  <EMPLOYER>
    <DOSSIER>2</DOSSIER>
    <SUMMARY>
      <BEGINDATE>2019-02-14</BEGINDATE>
      <WORKER>
        <NRWORKER>1</NRWORKER>
        <RESULT_DETAIL>
          <CODE>98765</CODE>
          <MINUTES>600</MINUTES>
          <CLASS>B</CLASS>
        </RESULT_DETAIL>
      </WORKER>
    </SUMMARY>
  </EMPLOYER>
</Data>' ) FROM DUAL UNION ALL
SELECT XMLTYPE( '<Data>
  <EMPLOYER>
    <DOSSIER>3</DOSSIER>
    <SUMMARY>
      <BEGINDATE>2019-02-14</BEGINDATE>
      <WORKER>
        <NRWORKER>7</NRWORKER>
      </WORKER>
    </SUMMARY>
  </EMPLOYER>
</Data>' ) FROM DUAL

查询：

SELECT Dossier,
       BeginDate,
       NRWorker,
       Code,
       Minutes,
       Class,
       CASE
       WHEN c2.RESULT_DETAIL IS NULL
            OR
            XMLEXISTS(
              '/RESULT_DETAIL/CLASS[not(text())][not(*)]'
              PASSING c2.RESULT_DETAIL
            )
       THEN 1
       ELSE 0
       END AS isClassEmpty,
       CASE WHEN Class IS NULL THEN 1 ELSE 0 END AS isClassEmpty2
FROM XML_TEST x
     LEFT OUTER JOIN
     XMLTABLE(
       '/Data/EMPLOYER'
       PASSING x.File_XML
       COLUMNS DOSSIER  NUMBER(8) PATH 'DOSSIER',
               SUMMARY  XMLTYPE   PATH 'SUMMARY'
     ) e
     ON ( 1 = 1 )
     LEFT OUTER JOIN
     XMLTABLE(
       '/SUMMARY'
       PASSING e.SUMMARY
       COLUMNS BEGINDATE DATE    PATH 'BEGINDATE',                            
               WORKER    XMLTYPE PATH 'WORKER'
     ) c1
     ON ( 1 = 1 )
     LEFT OUTER JOIN
     XMLTABLE(
       '/WORKER'
       PASSING c1.WORKER
       COLUMNS NRWORKER      NUMBER(7) PATH 'NRWORKER',                            
               RESULT_DETAIL XMLTYPE   PATH 'RESULT_DETAIL'
     ) c2
     ON ( 1 = 1 )
     LEFT OUTER JOIN
     XMLTABLE(
       '/RESULT_DETAIL'
       PASSING c2.RESULT_DETAIL
       COLUMNS CODE    CHAR(5)   PATH 'CODE',                            
               MINUTES NUMBER(5) PATH 'MINUTES',                            
               CLASS   CHAR(1)   PATH 'CLASS'                          
     ) c3
     ON ( 1 = 1 );

输出：

档案 |开始 | NR工人 |代码 |分钟 |课程 |分类 |分类2 ------: | :-------- | --------: | :---- | ------: | :---- | ------------: | ------------: 1 | 19 年 2 月 13 日 | 42 | 12345 | 0 | 空 | 1 | 1 2 | 19 年 2 月 14 日 | 1 | 98765 | 600 |乙| 0 | 0 3 | 19 年 2 月 14 日 | 7 | 空 | 空 | 空 | 1 | 1

db小提琴here

Answer 2

XMLEXISTS 确实对空元素返回 true，你只是发送它 c3.CLASS，这是一个 CHAR(1) 列而不是 XMLTYPE，因此它不会检测到根元素 (/ ) 并返回 false。

这里有一个例子，你可以用不同的方式来解决这个问题。我将 CLASS 的 XMLTYPE 副本添加到 c3，并在 SELECT 子句中引用它。尝试从示例数据或整个 CLASS 节点中删除“z”，看看会发生什么。

查看how to write an XPATH query to check if a node is empty 的类似问题。

-- sample data
with xml_test as (select xmltype('<Data><EMPLOYER><SUMMARY><WORKER><RESULT_DETAIL><CLASS>z</CLASS></RESULT_DETAIL></WORKER></SUMMARY></EMPLOYER></Data>') as file_xml from dual)
-- your query
SELECT --case when XMLEXISTS('/' passing by ref c3.class) then 1 else 0 end E_CLASS, /* won't work if CLASS is non-empty */
       case when XMLEXISTS('/' passing by ref c3.class_x) then 1 else 0 end E_CLASS_X,
       case when XMLEXISTS('/RESULT_DETAIL/CLASS' passing by ref c2.RESULT_DETAIL) then 1 else 0 end E_RD_CLASS,
       c3.CLASS, 
       c3.CLASS_X, 
       -- but this probably does what you want, detect if CLASS exists and is empty:
       case when XMLEXISTS('/CLASS' passing by ref c3.class_x)
             and not XMLEXISTS('/CLASS/text()' passing by ref c3.class_x) then 1 else 0 end EMPTY_CLASS
FROM XML_TEST x,
   XMLTABLE ('/Data/EMPLOYER'
                    PASSING x.File_XML
                    COLUMNS DOSSIER           NUMBER(8)       PATH     'DOSSIER',
                            SUMMARY           XMLTYPE         PATH 'SUMMARY'
            ) e,
   XMLTABLE ('/SUMMARY'
                PASSING e.SUMMARY
                COLUMNS BEGINDATE          DATE            PATH 'BEGINDATE',                            
                        WORKER             XMLTYPE         PATH 'WORKER'
            ) c1,
   XMLTABLE ('/WORKER'
                PASSING c1.WORKER
                COLUMNS NRWORKER           NUMBER(7)       PATH 'NRWORKER',                            
                        RESULT_DETAIL      XMLTYPE         PATH 'RESULT_DETAIL'
            ) c2 ,
    XMLTABLE ('/RESULT_DETAIL'
                PASSING c2.RESULT_DETAIL
                COLUMNS CODE               CHAR(5)         PATH 'CODE',                            
                        MINUTES            NUMBER(5)       PATH 'MINUTES',                            
                        CLASS              CHAR(1)         PATH 'CLASS',
                        CLASS_X            XMLTYPE         PATH 'CLASS'  -- added an XMLTYPE column with the same data                          
            ) c3 ;