Question

I have a stored proc that inserts XML into an underlying table. Unfortunately the XML passed in as a Sql XML type sometimes has particular elements missing. This makes the INSERT statement insert XML node values into the wrong columns.

My T-SQL looks something like this:

ALTER PROCEDURE [dbo].[up_Test_Insert]
    @xmlData XML
AS
BEGIN
INSERT INTO
TestTable
(
  ColumnA,
  ColumnB,
  ColumnC
)
SELECT
    Tbl.Col.value(ColumnA[1]', 'INT'),
    Tbl.Col.value('ColumnB[1]', 'INT'),
    Tbl.Col.value('ColumnC[1]', 'INT')
 FROM
   @xmlData.nodes('DocumentElement/DataTable') Tbl(Col) 

Sometimes ColumnB element may be missing in the XML structure. This results in the ColumnC node value being inserted into the ColumnB table column.

Is there a way to make the “value” operator return null on missing elements?

Answer 1

You have probably simplified your sample a bit too much. What you have here works as expected and will not insert ColumnC values to table ColumnA and missing ColumnB tags will give you a null value.

Try this:

declare @xmlData xml = '
<DocumentElement>
  <DataTable>
    <ColumnA>1</ColumnA>
    <ColumnC>3</ColumnC>
  </DataTable>
</DocumentElement>
'

SELECT
    Tbl.Col.value('ColumnA[1]', 'INT'),
    Tbl.Col.value('ColumnB[1]', 'INT'),
    Tbl.Col.value('ColumnC[1]', 'INT')
 FROM
   @xmlData.nodes('DocumentElement/DataTable') Tbl(Col) 

Result:

----------- ----------- -----------
1           NULL        3