使用 Oracle pl/sql 从具有命名空间的 xml clob 中提取值

Question

我目前正在尝试从 clob 列中提取值，但得到的结果总是 null。

我尝试了很多可能的场景，但对我来说它总是返回 null。

附上实物xml

<TenderOffer xmlns="http://xmlns.oracle.com/apps/otm">
    <Shipment>
        <ShipmentHeader/>
        <SEquipment/>
        <ShipmentStop/>
        <ShipmentStop/>
        <Location/>
        <Location/>
        <Release/>
        <RATE_OFFERING>
            <RATE_OFFERING_ROW>
                <USER_CLASSIFICATION3>ZXF</USER_CLASSIFICATION3>
            </RATE_OFFERING_ROW>
        </RATE_OFFERING>
    </Shipment>
    </TenderOffer>

以下是实际查询，

select 
        itc.element_name,
        extractvalue(XMLTYPE(XML_BLOB), '/TenderOffer/Shipment/RATE_OFFERING/RATE_OFFERING_ROW/USER_CLASSIFICATION3/text()'),
    XMLTYPE(XML_BLOB)
        from i_transaction itc
        where itc.i_transaction_no = 31553115
            and rownum = 1

Answer 1

在您的代码中，您使用 XML_BLOB 作为变量 - 所以我假设了 BLOB 数据类型，需要转换为 CLOB。但是，如果您有一个 CLOB 值，那么您可以跳过使用 BLOB_TO_CLOB 函数：

Oracle 11 设置:

CREATE OR REPLACE FUNCTION BLOB_TO_CLOB( b BLOB )
RETURN CLOB 
IS
  c            CLOB;
  n            INTEGER     := 1;
  w   CONSTANT PLS_INTEGER := 32767;
  len CONSTANT INTEGER     := LENGTH( b );
BEGIN
  IF b IS NULL THEN
    RETURN NULL;
  END IF;

  IF len = 0 THEN
    RETURN EMPTY_CLOB();
  END IF;

  DBMS_LOB.CREATETEMPORARY( c, TRUE );
  WHILE ( n + w <= len ) LOOP
    DBMS_LOB.WRITEAPPEND( c, w, UTL_RAW.CAST_TO_VARCHAR2( DBMS_LOB.SUBSTR( b, w, n ) ) );
    n := n + w;
  END LOOP;
  DBMS_LOB.WRITEAPPEND( c, len - n + 1, UTL_RAW.CAST_TO_VARCHAR2( DBMS_LOB.SUBSTR( b, len - n + 1, n ) ) );
  RETURN c;
END;
/

CREATE TABLE blob_test ( value BLOB );

INSERT INTO blob_test VALUES (
  UTL_RAW.CAST_TO_RAW(
    '<Header>' ||
      '<SecondHeader>' ||
        '<ThirdHeader>' ||
          '<FourthHeader>' ||
            '<Value1>abcd</Value1>' ||
            '<Value2>xyz</Value2>' ||
            '<Value3>abxy</Value3>' ||
          '</FourthHeader>' ||
        '</ThirdHeader>' ||
      '</SecondHeader>' ||
    '</Header>'
  )
);

查询:

EXTRACT 和 EXTRACTVALUE 已弃用 - 请改用 XMLTABLE：

SELECT Value1, Value2, Value3
FROM   blob_test b
       CROSS JOIN
       XMLTABLE(
         '/Header/SecondHeader/ThirdHeader/FourthHeader'
         PASSING XMLTYPE( BLOB_TO_CLOB( b.value ) )
         COLUMNS Value1 VARCHAR2(50) PATH 'Value1/text()',
                 Value2 VARCHAR2(50) PATH 'Value2/text()',
                 Value3 VARCHAR2(50) PATH 'Value3/text()'
       ) x;

输出:

VALUE1 VALUE2 VALUE3
------ ------ ------
abcd   xyz    abxy

查询 2:

如果您确实想使用 EXTRACTVALUE，您可以从 XPath 中删除 /text()，因为 EXTRACTVALUE 会为您完成（但它仍然可以在那里使用）并将 BLOB 转换为 CLOB:

SELECT EXTRACTVALUE(
         XMLTYPE( BLOB_TO_CLOB( value ) ), 
         '/Header/SecondHeader/ThirdHeader/FourthHeader/Value3'
       )
FROM   blob_test

查询 - 更新:

@AlexPoole. The call to BLOB_TO_CLOB is not necessary as the XMLTYPE constructor 的简化可以采用 BLOB 和字符集 ID：

SELECT Value1, Value2, Value3
FROM   blob_test b
       CROSS JOIN
       XMLTABLE(
         '/Header/SecondHeader/ThirdHeader/FourthHeader'
         PASSING XMLTYPE( b.value, NLS_CHARSET_ID('UTF8') )
         COLUMNS Value1 VARCHAR2(50) PATH 'Value1/text()',
                 Value2 VARCHAR2(50) PATH 'Value2/text()',
                 Value3 VARCHAR2(50) PATH 'Value3/text()'
       ) x;

Answer 2

您更新后的 XML 有一个命名空间，这最终揭示了问题。您需要 specify the namespace as part of the XML extraction，使用 XMLTable 方法更简单；在这种情况下，您可以将其视为默认命名空间：

select itc.element_name, x.user_classification3
from i_transaction itc
cross join xmltable(
  xmlnamespaces(default 'http://xmlns.oracle.com/apps/otm'),
    '/TenderOffer/Shipment/RATE_OFFERING/RATE_OFFERING_ROW'
  passing xmltype(itc.xml_blob)
  columns user_classification3 varchar2(10) path 'USER_CLASSIFICATION3'
) x
where itc.i_transaction_no = 31553115
and rownum = 1;

ELEMENT_NA USER_CLASS
---------- ----------
dummy      ZXF

或使用XML查询：

select itc.element_name, xmlquery(
  'declare default element namespace "http://xmlns.oracle.com/apps/otm"; (: :)
    /TenderOffer/Shipment/RATE_OFFERING/RATE_OFFERING_ROW/USER_CLASSIFICATION3/text()'
  passing xmltype(itc.xml_blob)
  returning content
) x
from i_transaction itc
where itc.i_transaction_no = 31553115
and rownum = 1;

ELEMENT_NA X                                                                               
---------- --------------------------------------------------------------------------------
dummy      ZXF

如果您想继续使用已弃用的 extractvalue() 函数，您也可以再次将命名空间作为参数提供给它 as shown in the documentation:

select itc.element_name,
  extractvalue(xmltype(xml_blob),
    '/TenderOffer/Shipment/RATE_OFFERING/RATE_OFFERING_ROW/USER_CLASSIFICATION3/text()',
    'xmlns="http://xmlns.oracle.com/apps/otm"')
from i_transaction itc where itc.i_transaction_no = 31553115 and rownum = 1;

使用 Oracle pl/sql 从具有命名空间的 xml clob 中提取值

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