Need to update multiple nodes in a XML string using values from an SQL query

The XML-method .modify() allows for one change at a time. This would mean to use one statement per needed change. A CURSOR or a WHILE loop might be a good idea.

As I try to avoid procedural logic, you can have a look at these alternatives:

Shred and re-create

One approach was to shred the whole thing and recreate it from scratch:

First I create a mockup to simulate your situation

DECLARE @DocList XML=
N'<JobList ListItems="7">
  <Job JobFriendlyName="EMAIL INVOICES">
    <DocumentList>
      <Document Doc="1" ID="5280301.2019050148902.00020" Date="05-03-2019" Status="NEW" />
      <Document Doc="2" ID="5280301.2019050148902.00022" Date="05-03-2019" Status="NEW" />
      <Document Doc="3" ID="5280301.2019050148902.00023" Date="05-03-2019" Status="NEW" />
      <Document Doc="4" ID="5280301.2019050104301.00055" Date="05-02-2019" Status="NEW" />
      <Document Doc="5" ID="5280301.2019050104301.00056" Date="05-02-2019" Status="NEW" />
    </DocumentList>
  </Job>
  <Job JobFriendlyName="INVOICES">
    <DocumentList>
      <Document Doc="6" ID="5280300.2019050148901.00001" Date="05-03-2019" Status="NEW" />
      <Document Doc="7" ID="5280300.2019050148901.00002" Date="05-03-2019" Status="NEW" />
    </DocumentList>
  </Job>
</JobList>';

DECLARE @mockupDocAccess TABLE
(
    [Key] varchar(10),
    [DocIDNumber] [varchar](35),
    [DocLastOpenDtg] [smalldatetime]
);

INSERT INTO @mockupDocAccess VALUES('SomeKey','5280301.2019050148902.00022',GETDATE())   --Doc 2
                                  ,('SomeKey','5280301.2019050104301.00055',GETDATE())   --Doc 4
                                  ,('SomeKey','5280300.2019050148901.00001',GETDATE())   --Doc 6
                                  ,('OtherKey','5280301.2019050104301.00056',GETDATE()); --Doc 5

--Now we can read all values from the XML and re-create the XML after using CASE to set the needed status values to OLD:

DECLARE @Key VARCHAR(10)='SomeKey';

WITH AllEmailInvoices AS
(
    SELECT d.value('@Doc','int') AS Doc
          ,d.value('@ID','nvarchar(35)') AS ID
          ,d.value('@Date','nvarchar(10)') AS [Date] --unconverted
          ,CASE WHEN EXISTS(SELECT 1 FROM @mockupDocAccess da WHERE da.DocIDNumber=d.value('@ID','nvarchar(35)') AND da.[Key]=@Key) THEN 'OLD' ELSE d.value('@Status','nvarchar(10)') END AS [Status]
 
    FROM @DocList.nodes('/JobList/Job[@JobFriendlyName="EMAIL INVOICES"]/DocumentList/Document') A(d)
)
,AllInvoices AS
(
    SELECT d.value('@Doc','int') AS Doc
          ,d.value('@ID','nvarchar(35)') AS ID
          ,d.value('@Date','nvarchar(10)') AS [Date] --unconverted
          ,CASE WHEN EXISTS(SELECT 1 FROM @mockupDocAccess da WHERE da.DocIDNumber=d.value('@ID','nvarchar(35)') AND da.[Key]=@Key) THEN 'OLD' ELSE d.value('@Status','nvarchar(10)') END AS [Status]
 
    FROM @DocList.nodes('/JobList/Job[@JobFriendlyName="INVOICES"]/DocumentList/Document') A(d)
)
SELECT @DocList.value('(/JobList/@ListItems)[1]','int') AS [@ListItems]
      ,(
            SELECT 'EMAIL INVOICES' AS [@JobFriendlyName]
                   ,(
                        SELECT Doc AS [@Doc]
                              ,ID AS [@ID]
                              ,[Date] AS [@Date]
                              ,[Status] AS [@Status]      
                        FROM AllEmailInvoices
                        FOR XML PATH('Document'),ROOT('DocumentList'),TYPE
                    )
            FOR XML PATH('Job'),TYPE
        )
        ,(
            SELECT 'INVOICES' AS [@JobFriendlyName]
                   ,(
                        SELECT Doc AS [@Doc]
                              ,ID AS [@ID]
                              ,[Date] AS [@Date]
                              ,[Status] AS [@Status]      
                        FROM AllInvoices
                        FOR XML PATH('Document'),ROOT('DocumentList'),TYPE
                    )
            FOR XML PATH('Job'),TYPE
        )
FOR XML PATH('JobList');

XQuery and FLWOR approach

Alternatively you can try something along this:

DECLARE @Key VARCHAR(10)='SomeKey';

SELECT
(
    SELECT (SELECT DocIDNumber AS ID FROM @mockupDocAccess WHERE [Key]=@Key FOR XML PATH(''),TYPE) DocAccess
          ,@DocList
    FOR XML PATH(''),TYPE
).query
(N'
    <JobList> {/JobList/@*}
    {
    for $j in /JobList/Job 
    return
        <Job> {$j/@*}
        {
            <DocumentList>
            {
            for $d in $j/DocumentList/Document
            return
                <Document Doc="{$d/@Doc}" 
                          ID="{$d/@ID}" 
                          Date="{$d/@Date}" 
                          Status="{if(/DocAccess[ID=$d/@ID]) then "OLD" else xs:string($d/@Status)}" />
            }
            </DocumentList>
        }
        </Job>
    }
    </JobList>
');

First we create a XML where we include the values from the DocAccess-table. This will look like this:

<DocAccess>
  <ID>5280301.2019050148902.00022</ID>
  <ID>5280301.2019050104301.00055</ID>
  <ID>5280300.2019050148901.00001</ID>
</DocAccess>
<JobList ListItems="7">
  <!-- Your Content here -->
</JobList>

The XQuery will rebuild the document but will set the Status-attribute depending on the existance of a corresponding ID element in <DocAccess>.

Final statement

You can use a

• CURSOR with separate statemets per change,
• you can shred and re-create the XML or
• you can use XQuery/FLWOR to re-build the XML.

It depends on your needs, which approach you prefer.