sql query xml values returning NULL

问题

I'm not experienced with the xml structure and need a start-point to how I can retrieve the values from xml structure below.

I fetch the xml from a webservice using a stored-procedure and store to a table "StockInfoXML" Field in table holding the xml is XML_Url of type xml.

<string xmlns="http://www.webserviceX.NET/">
  <StockQuotes>
    <Stock>
      <Symbol>ENGI.PA</Symbol>
      <Last>13.53</Last>
      <Date>5/23/2017</Date>
      <Time>12:37pm</Time>
      <Change>+0.06</Change>
      <Open>13.45</Open>
      <High>13.59</High>
      <Low>13.40</Low>
      <Volume>1524437</Volume>
      <MktCap>32.95B</MktCap>
      <PreviousClose>13.47</PreviousClose>
      <PercentageChange>+0.48%</PercentageChange>
      <AnnRange>10.77 - 15.20</AnnRange>
      <Earns>-0.23</Earns>
      <P-E>N/A</P-E>
      <Name>ENGIE</Name>
    </Stock>
  </StockQuotes>
</string>

I've tried a couple of things but keep returning null or nothing.

declare @X XML;

SELECT
@X = XML_Url
FROM dbo.StockExchangeInfoXML

SELECT 
x.s.value('(StockQuotes/Stock/Symbol)[1]', 'nvarchar(50)') AS [Symbol]
FROM @X.nodes('./StockQuotes/Stock') AS x(s);

Anyone who can get me started? Thanks.

回答1:

Your xml includes a namespace xmlns="http://www.webserviceX.NET/", which is the default namespace. You must either declare it or use a wildcard for the prefix.

With XML there are some best practices:

Be as specific as possible
Only forward navigation
Important If the creation of the XML is under your control change the date and time format to ISO8601. Your formats are culture specific and can easily lead to conversion errors on different systems. Best was a combined value like <DateAndTime>2017-05-23T12:37:00</DateAndTime>

For your issue there are several approaches:

DECLARE @xml XML=
N'<string xmlns="http://www.webserviceX.NET/">
  <StockQuotes>
    <Stock>
      <Symbol>ENGI.PA</Symbol>
      <Last>13.53</Last>
      <Date>5/23/2017</Date>
      <Time>12:37pm</Time>
      <!--more elements -->
    </Stock>
  </StockQuotes>
</string>';

--Best approach: XMLNAMESPACES to declare the default namespace

WITH XMLNAMESPACES(DEFAULT 'http://www.webserviceX.NET/')
SELECT @xml.value(N'(/string/StockQuotes/Stock/Symbol/text())[1]',N'nvarchar(max)');

--Implicit namespace declaration:

SELECT @xml.value(N'declare namespace ns="http://www.webserviceX.NET/";
                   (/ns:string/ns:StockQuotes/ns:Stock/ns:Symbol/text())[1]',N'nvarchar(max)');

--Not recommended in most cases, but good for lazy people :-D

SELECT @xml.value(N'(//*:Symbol)[1]',N'nvarchar(max)');

--If you want to read more values of the same level, you can use .nodes to set the current node to ...<Stock>.

WITH XMLNAMESPACES(DEFAULT 'http://www.webserviceX.NET/')
SELECT st.value('(Symbol/text())[1]',N'nvarchar(max)')
      ,st.value('(Last/text())[1]',N'decimal(10,4)')
      --more nodes 
FROM @xml.nodes(N'/string/StockQuotes/Stock') AS A(st);

回答2:

You must set namespace for xml before get value

DECLARE @xml XML = N'<string xmlns="http://www.webserviceX.NET/">
  <StockQuotes>
    <Stock>
      <Symbol>ENGI.PA</Symbol>
      <Last>13.53</Last>
      <Date>5/23/2017</Date>
      <Time>12:37pm</Time>
      <Change>+0.06</Change>
      <Open>13.45</Open>
      <High>13.59</High>
      <Low>13.40</Low>
      <Volume>1524437</Volume>
      <MktCap>32.95B</MktCap>
      <PreviousClose>13.47</PreviousClose>
      <PercentageChange>+0.48%</PercentageChange>
      <AnnRange>10.77 - 15.20</AnnRange>
      <Earns>-0.23</Earns>
      <P-E>N/A</P-E>
      <Name>ENGIE</Name>
    </Stock>
  </StockQuotes>
</string>'

;WITH XMLNAMESPACES('http://www.webserviceX.NET/' as ns)
SELECT 
x.s.value('(./ns:Symbol)[1]', 'varchar(50)') AS [Symbol]
FROM @xml.nodes('/ns:string/ns:StockQuotes/ns:Stock') AS x(s);

Returns

Symbol
--------
ENGI.PA

来源：https://stackoverflow.com/questions/44156552/sql-query-xml-values-returning-null

标签

xml

sql-server-2012