尝试使用 SQL Server 中的查询从表列访问 XML 节点值，它总是返回一个空字符串

Question

有一个名为UserRequest 的表，其中一列是XML 类型（列名是RequestXML）。 RequestXML 中的值将是这样的：

<MyRequest xmlns:i="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://schemas.datacontract.org/2004/07/">
    <transfer>
        <Field>
            <fieldId>12323</fieldId>
            <FieldDetails>
                <RequestInfoField>
                    <requestDecs>Test</requestDecs>
                    <reqDate>01/01/2021</reqDate>
                </RequestInfoField>
                <identifierKey>45638</identifierKey>
            </FieldDetails>
        </Field>
    </transfer>
</MyRequest>

使用以下 SQL 查询检索 XML 节点值identifierKey，但查询始终返回空字符串：

select 
    T.RequestXML.query('MyRequest/transfer/Field/FieldDetails/identifierKey') As identifierKey, * 
from UserRequest  T

Answer 1

您尚未在 SQL 中声明您的（默认）命名空间：

WITH XMLNAMESPACES(DEFAULT 'http://schemas.datacontract.org/2004/07/')
SELECT UR.RequestXML.query('MyRequest/transfer/Field/FieldDetails/identifierKey') As identifierKey,
       *
FROM dbo.UserRequest UR;

但是，如果您明确想要 identifierKey 的值，请使用 value，而不是 query。

WITH XMLNAMESPACES(DEFAULT 'http://schemas.datacontract.org/2004/07/')
SELECT UR.RequestXML.value('(MyRequest/transfer/Field/FieldDetails/identifierKey)[1]','int') AS identifierKey
       *
FROM dbo.UserRequest UR;

db<>fiddle

Answer 2

像这样：

declare @doc xml = '<MyRequest xmlns:i="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://schemas.datacontract.org/2004/07/">
    <transfer>
        <Field>
            <fieldId>12323</fieldId>
            <FieldDetails>
                <RequestInfoField>
                    <requestDecs>Test</requestDecs>
                    <reqDate>01/01/2021</reqDate>
                </RequestInfoField>
                <identifierKey>45638</identifierKey>
            </FieldDetails>
        </Field>
    </transfer>
</MyRequest>';

WITH XMLNAMESPACES(DEFAULT 'http://schemas.datacontract.org/2004/07/')
SELECT T.RequestXML.value('(/MyRequest/transfer/Field/FieldDetails/identifierKey)[1]','int') As identifierKey,  *
FROM (values(@doc)) T(RequestXML);