SQL - Read XML node value from attribute name

Question

I have a column that contains an XML like this:

<metadata>
   <meta id="TypeX" valuetype="xs:string">
      <values>
         <value>3</value>
      </values>
   </meta>
   <meta id="TypeY" valuetype="xs:string">
      <values>
         <value>5</value>
      </values>
   </meta>
</metadata>

and I need to query it by meta Tag Attribute 'id'.

I need to have foreach 'meta' tag his id and value.

Answer 1

here you have something that should help:

declare @xml xml

set @xml = '<metadata>
   <meta id="TypeX" valuetype="xs:string">
      <values>
         <value>3</value>
      </values>
   </meta>
   <meta id="TypeY" valuetype="xs:string">
      <values>
         <value>5</value>
      </values>
   </meta>
</metadata>'

select C.value('(./@id)', 'varchar(5)') AS [Meta ID]
     , C.value('(./values/value)[1]', 'tinyint') AS [Value]
from @xml.nodes('/metadata/meta') AS T(C)

Moreover, it could be useful for you to get familiar with XQueries :)

You can change data type in select statement from varchar(5) to some bigger varchar or from tinyint to some "bigger" type, if you need to.

Best regards.

Answer 2

If your XML is big, it will lead to a bad performance, if you first shred the whole thing, just to filter it afterwards. It is better to include your filter as predicate into your XQuery :

DECLARE @xml XML=
N'<metadata>
   <meta id="TypeX" valuetype="xs:string">
      <values>
         <value>3</value>
      </values>
   </meta>
   <meta id="TypeY" valuetype="xs:string">
      <values>
         <value>5</value>
         <value>6</value>
      </values>
   </meta>
</metadata>';

--This is the variable holding the id's value

DECLARE @id VARCHAR(10)='TypeX';

--This SELECT reads the first <value> within <values> as one-liner :

SELECT @xml.value(N'(/metadata/meta[@id=sql:variable("@id")]/values/value/text())[1]','int'); 

--Change the filter-variable

SET @id='TypeY'

--This query will use .nodes() to get all <value> nodes within <values> (if there are more of them)

SELECT v.value('text()[1]','int')
FROM @xml.nodes(N'/metadata/meta[@id=sql:variable("@id")]/values/value') AS A(v); 

One more hint: If you are sure, that there is only one entry per @id , you might extend the predicate to [@id=sql:variable("@id")][1] . This will prevent the engine to continue searching for nodes with this id.