Querying one to many relationship in an XML Column - tsql

Question

I have an XML column in a table.
The table looks has two columns:
ID
DepartmentXML
The DepartmentXML typically looks like this:
<Root>
<Department>
<dID>100</dID>
<DName>Engineering</DName>
</Department>
<Employee>
<EmployeeID>999</EmployeeID>
<EName>AAA BBB</EName>
</Employee>
<Employee>
<EmployeeID>888</EmployeeID>
<EName>XXX YYY</EName>
</Employee>
</Root>
How to query this XML, to get result like this?
+------------------------------------------+
|dID|DepartmentName|EmployeeID|EmployeeName|
+------------------------------------------+
|100|Engineering |999 |AAA BBB |
|100|Engineering |888 |XXX YYY |
+------------------------------------------+
I know CROSS APPLY may have to be used, but the syntax for this particular scenario is very difficult for me to understand.
Thank you.

Answer 1

Try it like this:
First a mockup table to simulate your issue:
DECLARE #tbl TABLE(ID INT IDENTITY, DepartmentXml XML);
INSERT INTO #tbl VALUES
(N'<Root>
<Department>
<dID>100</dID>
<DName>Engineering</DName>
</Department>
<Employee>
<EmployeeID>999</EmployeeID>
<EName>AAA BBB</EName>
</Employee>
<Employee>
<EmployeeID>888</EmployeeID>
<EName>XXX YYY</EName>
</Employee>
</Root>');
--The query
SELECT t.ID
,t.DepartmentXml.value('(/Root/Department/dID/text())[1]','int') AS DepartmentId
,t.DepartmentXml.value('(/Root/Department/DName/text())[1]','nvarchar(max)') AS DepartmentName
,A.e.value('(EmployeeID/text())[1]','int') AS EmployeeId
,A.e.value('(EName/text())[1]','nvarchar(max)') AS EmployeeName
FROM #tbl t
OUTER APPLY t.DepartmentXml.nodes('/Root/Employee') A(e);
The idea in short:
We can pick the row's ID directly
We can read the department's information directly from the XML (non-repeating)
We can retrieve repeating nodes using APPLY with .nodes().
We can use a relative XPath against A.e to get the employee's data