问：如何从XSD字符串字段中选择命名元素值

编程问答 2022-11-01

问题描述

在sql Server中，我试图从XSD字符串中选择值。

例如给出以下sql Server表

CREATE TABLE dbo.textxML (
ID INT PRIMARY KEY,Data NVARCHAR(max))

INSERT INTO dbo.textxML ( ID,Data )
SELECT 1,('<element name="Rownum" value="Row23" />
          <element name="CONNECTIONTYPESECTION" value="True" />
          <element name="CustomFields" />
          <element name="EchoData">
            <element name="0000" value="8220000000000000" />
            <element name="0001" value="0400000100000000" />
            <element name="0007" value="0805193143" />
            <element name="MessageType" value="1234" />
          </element>
          <element name="ENABLESSL" value="false" />' )

INSERT INTO dbo.textxML ( ID,Data )
SELECT 2,('<element name="Rownum" value="Row24" />
      <element name="CONNECTIONTYPESECTION" value="True" />
      <element name="CustomFields" />
      <element name="EchoData">
        <element name="0000" value="8220000000000000" />
        <element name="0001" value="0400000100000000" />
        <element name="0007" value="0805193143" />
        <element name="MessageType" value="5678" />
      </element>
      <element name="ENABLESSL" value="true" />' );

我希望能够为给定的元素名称选择值。像... 

SELECT ID,Data.CONNECTIONTYPESECTION,Data.EchoData.0007,Data.EchoData.MessageType,Data.ENABLESSL
FROM textxML
WHERE Data.Rownum = "Row23" AND Data.EchoData.MessageType = "1234".

ID  Data.CONNECTIONTYPESECTION Data.EchoData.0007 Data.EchoData.MessageType Data.ENABLESSL
1   True                       0805193143         1234                      true

我可以使用CHARINDEX和SUBSTRING，但必须对“ 名称”值的长度进行硬编码，并且假定“ 值”的长度始终相同。我希望有一种更好，更有效的方法来做到这一点。

我已经尝试了CROSS APPPLY和XML VALUE函数，但这仅返回Data字段中的第一个元素。我也找不到如何搜索特定元素“ 名称”以获取其值

解决方法

请尝试以下T-SQL。

-- DDL and sample data population,start
DECLARE @tbl TABLE (ID INT IDENTITY PRIMARY KEY,Data NVARCHAR(max));
INSERT INTO @tbl (Data) VALUES
(N'<element name="Rownum" value="Row23"/>
    <element name="CONNECTIONTYPESECTION" value="True"/>
    <element name="CustomFields"/>
    <element name="EchoData">
        <element name="0000" value="8220000000000000"/>
        <element name="0001" value="0400000100000000"/>
        <element name="0007" value="0805193143"/>
        <element name="MessageType" value="1234"/>
    </element>
    <element name="ENABLESSL" value="false"/>'),(N'<element name="Rownum" value="Row24"/>
    <element name="CONNECTIONTYPESECTION" value="True"/>
    <element name="CustomFields"/>
    <element name="EchoData">
        <element name="0000" value="8220000000000000"/>
        <element name="0001" value="0400000100000000"/>
        <element name="0007" value="0805193143"/>
        <element name="MessageType" value="5678"/>
    </element>
    <element name="ENABLESSL" value="true"/>');
-- DDL and sample data population,end

;WITH rs AS
(
    SELECT *,TRY_CAST(data AS XML) AS xmldata
    FROM @tbl
)
SELECT rs.ID,xmldata.value('(element[@name="CONNECTIONTYPESECTION"]/@value)[1]','VARCHAR(10)') AS CONNECTIONTYPESECTION,xmldata.value('(element[@name="EchoData"]/element[@name="0007"]/@value)[1]','VARCHAR(10)') AS [EchoData.0007],xmldata.value('(element[@name="EchoData"]/element[@name="MessageType"]/@value)[1]','VARCHAR(10)') AS [EchoData.MessageType],xmldata.value('(element[@name="ENABLESSL"]/@value)[1]','VARCHAR(10)') AS [Data.ENABLESSL]
FROM rs
WHERE xmldata.value('(element[@name="Rownum"]/@value)[1]','VARCHAR(30)') = 'Row23'
    AND xmldata.value('(element[@name="EchoData"]/element[@name="MessageType"]/@value)[1]','VARCHAR(10)') = '1234';

输出 

+----+-----------------------+---------------+----------------------+----------------+
| ID | CONNECTIONTYPESECTION | EchoData.0007 | EchoData.MessageType | Data.ENABLESSL |
+----+-----------------------+---------------+----------------------+----------------+
|  1 | True                  |    0805193143 |                 1234 | false          |
+----+-----------------------+---------------+----------------------+----------------+
sqlsqlsql-server-2017xmlxmlxmlxmlxmlxmlxsdxsdxsd