sql server - XPath to fetch SQL XML value

Question

Here is my problem: from the following XML that is within a column, I want to know if the value of a variable with the name 'Enabled' is equal to 'Yes' given a step Id and a component Id.

'<xml>
  <box stepId="1">
    <components>
      <component id="2">
        <variables>
          <variable id="3" nom="Server" valeur="DEV1" />
          <variable id="4" nom="Enabled" valeur="Yes" />
        </variables>
      </component>
      <component id="3">
        <variables>
          <variable id="3" nom="Server" valeur="DEV1" />
          <variable id="4" nom="Enabled" valeur="No" />
        </variables>
      </component>
    </components>
  </box>
  <box stepId="2">
    <components>
      <component id="2">
        <variables>
          <variable id="3" nom="Server" valeur="DEV2" />
          <variable id="4" nom="Enabled" valeur="Yes" />
        </variables>
      </component>
      <component id="3">
        <variables>
          <variable id="3" nom="Server" valeur="DEV2" />
          <variable id="4" nom="Enabled" valeur="No" />
        </variables>
      </component>
    </components>
  </box>
</xml>'

Answer 1

• XQuery Against the xml Data Type
• General XQuery Use Cases
• XQueries Involving Hierarchy

• XQueries Involving Order

• Anything in Michael Rys blog

Update

My recomendation would be to shred the XML into relations and do searches and joins on the resulted relation, in a set oriented fashion, rather than the procedural fashion of searching specific nodes in the XML. Here is a simple XML query that shreds out the nodes and attributes of interest:

select x.value(N'../../../../@stepId', N'int') as StepID
  , x.value(N'../../@id', N'int') as ComponentID
  , x.value(N'@nom',N'nvarchar(100)') as Nom
  , x.value(N'@valeur', N'nvarchar(100)') as Valeur
from @x.nodes(N'/xml/box/components/component/variables/variable') t(x)

However, if you must use an XPath that retrieves exactly the value of interest:

select x.value(N'@valeur', N'nvarchar(100)') as Valeur
from @x.nodes(N'/xml/box[@stepId=sql:variable("@stepID")]/
    components/component[@id = sql:variable("@componentID")]/
       variables/variable[@nom="Enabled"]') t(x)

If the stepID and component ID are columns, not variables, the you should use sql:column() instead of sql:variable in the XPath filters. See Binding Relational Data Inside XML Data.

And finaly if all you need is to check for existance you can use the exist() XML method:

select @x.exist(
  N'/xml/box[@stepId=sql:variable("@stepID")]/
    components/component[@id = sql:variable("@componentID")]/
      variables/variable[@nom="Enabled" and @valeur="Yes"]')