Question

I have the following XML structure

<?xml version="1.0" encoding="utf-8"?>
<DataItems>
    <DataItem>
        <ID>ID1</ID>
        <Metric1>Metric11Value</Metric1>
        <Metric2>Metric12Value</Metric2>
        <OptionalParameters>
           <OptionalParameter>
              <ParameterName>ParamName1</ParameterName>
              <ParameterValue>ParamValue1</ParameterValue>
              <ParameterUnits>ParamUnits1</ParameterUnits>
           <OptionalParamter> 
           <OptionalParameter>
              <ParameterName>ParamName2</ParameterName>
              <ParameterValue>ParamValue2</ParameterValue>
              <ParameterUnits>ParamUnits2</ParameterUnits>
           <OptionalParamter>
           <OptionalParameter>
              <ParameterName>ParamName3</ParameterName>
              <ParameterValue>ParamValue3</ParameterValue>
              <ParameterUnits>ParamUnits3</ParameterUnits>
           <OptionalParamter>
        </OptionalParamters>
    <DataItem>
        <ID>ID2</ID>
        <Metric1>Metric21Value</Metric1>
        <Metric2>Metric22Value</Metric2>
        <OptionalParameters>
           <OptionalParameter>
              <ParameterName>ParamName1</ParameterName>
              <ParameterValue>ParamValue1</ParameterValue>
              <ParameterUnits>ParamUnits1</ParameterUnits>
           <OptionalParamter> 
           <OptionalParameter>
              <ParameterName>ParamName2</ParameterName>
              <ParameterValue>ParamValue2</ParameterValue>
              <ParameterUnits>ParamUnits2</ParameterUnits>
           <OptionalParamter>
           <OptionalParameter>
              <ParameterName>ParamName3</ParameterName>
              <ParameterValue>ParamValue3</ParameterValue>
              <ParameterUnits>ParamUnits3</ParameterUnits>
           <OptionalParamter>
        </OptionalParamters>
    <DataItem>
</DataItems>

I would like to flatten it in a fashion that will give me a table row like

(ID, Metric1, Metric2, ParamName, ParamValue, ParamUnits)

The problem is that I don’t know how do peform the dynamic filtering I need in order to eliminate the invalid rows that result during the inner join or cross apply. So what I have essentially a total of (Number of Data Items)^2 of rows with all the permutations of parameters names, values, and units. I want to know how to filter out the invalid rows.

Answer 1

I think your XML is messed up. You have a bunch of open XML elements that do not have matching close elements. If you fix that, then it is easy to get the flattened output you want:

declare @idoc int, @xml varchar(max) = '
<?xml version="1.0" encoding="utf-8"?>
<DataItems>
  <DataItem>
    <ID>ID1</ID>
    <Metric1>Metric11Value</Metric1>
    <Metric2>Metric12Value</Metric2>
    <OptionalParameters>
      <OptionalParameter>
        <ParameterName>ParamName1</ParameterName>
        <ParameterValue>ParamValue1</ParameterValue>
        <ParameterUnits>ParamUnits1</ParameterUnits>
      </OptionalParameter>
    </OptionalParameters>
    <OptionalParameters>
      <OptionalParameter>
        <ParameterName>ParamName2</ParameterName>
        <ParameterValue>ParamValue2</ParameterValue>
        <ParameterUnits>ParamUnits2</ParameterUnits>
      </OptionalParameter>
    </OptionalParameters>
    <OptionalParameters>
      <OptionalParameter>
        <ParameterName>ParamName3</ParameterName>
        <ParameterValue>ParamValue3</ParameterValue>
        <ParameterUnits>ParamUnits3</ParameterUnits>
      </OptionalParameter>
    </OptionalParameters>
  </DataItem>
  <DataItem>
    <ID>ID2</ID>
    <Metric1>Metric21Value</Metric1>
    <Metric2>Metric22Value</Metric2>
    <OptionalParameters>
      <OptionalParameter>
        <ParameterName>ParamName1</ParameterName>
        <ParameterValue>ParamValue1</ParameterValue>
        <ParameterUnits>ParamUnits1</ParameterUnits>
      </OptionalParameter>
    </OptionalParameters>
    <OptionalParameters>
      <OptionalParameter>
        <ParameterName>ParamName2</ParameterName>
        <ParameterValue>ParamValue2</ParameterValue>
        <ParameterUnits>ParamUnits2</ParameterUnits>
      </OptionalParameter>
    </OptionalParameters>
    <OptionalParameters>
      <OptionalParameter>
        <ParameterName>ParamName3</ParameterName>
        <ParameterValue>ParamValue3</ParameterValue>
        <ParameterUnits>ParamUnits3</ParameterUnits>
      </OptionalParameter>
    </OptionalParameters>
  </DataItem>
</DataItems>'

exec sp_xml_preparedocument @idoc output, @xml

select *
from   openxml(@idoc, '/DataItems/DataItem/OptionalParameters/OptionalParameter', 1)
with   (
          ID varchar(5) '../../ID', 
          Metric1 varchar(18) '../../Metric1', 
          Metric2 varchar(20) '../../Metric2', 
          ParamName varchar(20) 'ParameterName', 
          ParameterValue varchar(20) 'ParameterValue',
          ParameterUnits varchar(20) 'ParameterUnits'
        )

exec sp_xml_removedocument @idoc
go

Which returns this:

ID    Metric1            Metric2              ParamName            ParameterValue       ParameterUnits
----- ------------------ -------------------- -------------------- -------------------- --------------------
ID1   Metric11Value      Metric12Value        ParamName1           ParamValue1          ParamUnits1
ID1   Metric11Value      Metric12Value        ParamName2           ParamValue2          ParamUnits2
ID1   Metric11Value      Metric12Value        ParamName3           ParamValue3          ParamUnits3
ID2   Metric21Value      Metric22Value        ParamName1           ParamValue1          ParamUnits1
ID2   Metric21Value      Metric22Value        ParamName2           ParamValue2          ParamUnits2
ID2   Metric21Value      Metric22Value        ParamName3           ParamValue3          ParamUnits3