Join XML columns from SQL Server 2016+ - sql-server

Question

I have a TABLE_A with an XML column mycategoryXML which contains this XML:
<mainxml>
<category id="1" ftype="1"/>
<category id="2" ftype="1"/>
<category id="3" ftype="1"/>
</mainxml>
I also have another TABLE_B with a XML column called mymappedids
<mapids>
<ids>
<myid id="1" name="Category Name1"/>
<myid id="2" name="Category Name2"/>
<myid id="3" name="Category Name3"/>
<myid id="4" name="Category Name4"/>
<myid id="5" name="Category Name5"/>
<myid id="6" name="Category Name6"/>
<myid id="7" name="Category Name7"/>
<myid id="8" name="Category Name8"/>
<myid id="9" name="Category Name9"/>
</ids>
</mapids>
Is it possible to select all Category nodes from TABLE_A and also the correct names for each category from table_B, so I ultimately get the follow result:
id | categoryid | categoryname
---+------------+-------------
1 | 1 | categoryname1
2 | 2 | categoryname2
3 | 3 | categoryname3
with one query from SQL Server?

Answer 1

There are several approaches but you did not tell us enough about your background.
Especially unclear: How is the connection between these two tables a and b?
You might try something along this:
A mockup scenario to simulate your issue (please provide this yourself in your next question):
DECLARE #tblA TABLE(aId INT,Xml1 XML);
DECLARE #tblB TABLE(bId INT,Xml2 XML);
INSERT INTO #tblA(aId,Xml1) VALUES
(100
,N'<mainxml>
<category id="1" ftype="1"/>
<category id="2" ftype="1"/>
<category id="3" ftype="1"/>
</mainxml>');
INSERT INTO #tblB(bId,Xml2) VALUES
(200
,N'<mapids>
<ids>
<myid id="1" name="Category Name1"/>
<myid id="2" name="Category Name2"/>
<myid id="3" name="Category Name3"/>
<myid id="4" name="Category Name4"/>
<myid id="5" name="Category Name5"/>
<myid id="6" name="Category Name6"/>
<myid id="7" name="Category Name7"/>
<myid id="8" name="Category Name8"/>
<myid id="9" name="Category Name9"/>
</ids>
</mapids>');
--The query
SELECT a.aId
,aXmlValues.*
,(SELECT Xml2.value('(/mapids
/ids
/myid[#id=sql:column("aXmlValues.CategoryId")]
/#name)[1]','nvarchar(max)')
FROM #tblB b
WHERE bID=200 /*however you find this...*/) AS CategoryName
FROM #tblA a
CROSS APPLY a.Xml1.nodes('/mainxml/category') aXml(c)
CROSS APPLY(SELECT aXml.c.value('#id','int') AS CategoryId
,aXml.c.value('#ftype','int') AS CategoryType) aXmlValues;
The idea in short:
We use APPLY ... .nodes() to get the categories of table "a" in separate rows (a derived set).
now we can use APPLY again. This is a trick to get the XML's value into the result set as a normal column.
This column can be placed into XQuery against table "b" using sql:column().

Answer 2

I assume you likely want something like this:
DECLARE #XML1 xml = '<mainxml>
<category id="1" ftype="1"/>
<category id="2" ftype="1"/>
<category id="3" ftype="1"/>
</mainxml>';
DECLARE #XML2 xml = '<mapids>
<ids>
<myid id="1" name="Category Name1"/>
<myid id="2" name="Category Name2"/>
<myid id="3" name="Category Name3"/>
<myid id="4" name="Category Name4"/>
<myid id="5" name="Category Name5"/>
<myid id="6" name="Category Name6"/>
<myid id="7" name="Category Name7"/>
<myid id="8" name="Category Name8"/>
<myid id="9" name="Category Name9"/>
</ids>
</mapids>';
SELECT X1.c.value('#id','int') AS id,
X2.mi.value('#id','int') AS categoryid, --Seem silly to have this value twice
X2.mi.value('#name','varchar(30)') AS categoryname
FROM (VALUES(#XML1)) V1(X)
CROSS APPLY (VALUES(#XML2)) V2(X)
CROSS APPLY V1.X.nodes('/mainxml/category')X1(c)
CROSS APPLY V2.X.nodes('/mapids/ids/myid')X2(mi)
WHERE X1.c.value('#id','int') = X2.mi.value('#id','int');