Converting a single XML bracket column to multiple columns in T-SQL SQL-SERVER - sql

Question

I've seen similar questions to mine but the XML format has always been different, as the XML format I have does not follow the "standard" strcuture. My table looks like the following (single column with XML bracket as row values):
|VAL|
|<person name="bob" age="22" city="new york" occupation="student"></person>|
|<person name="bob" age="22" city="new york" occupation="student"></person>|
And the outcome I'm looking for is:
|Name|age|city |occupation|
|bob |22 |new york|student |
|bob |22 |new york|student |
I can create hardcoded script with these column names, but the problem is that I have over 20 tables that would then all require a custom script. My thinking is that there is a way where I can dynamically, taken into account destination table and a source table (xml), I could have a procedure where this data is generated.

Answer 1

Your question is not all clear...
As far as I understand, you have a variety of different XMLs and you want to read them generically. If this is true, I'd suggest for your next question, to reflect this in your sample data.
One general statement is: There is no way around dynamically created statements, in cases, where you want to set the descriptive elements of a resultset (in this case: the names of the columns) dynamically. T-SQL relies on some things you must know in advance.
Try this:
I set up a mockup scenario to simulate your issue (please try to do this yourself in your next question):
DECLARE #tbl TABLE(ID INT IDENTITY, Descr VARCHAR(100), VAL XML);
INSERT INTO #tbl VALUES
('One person',N'|<person name="bob" age="22" city="new york" occupation="student"></person>')
,('One more person','<person name="bob" age="22" city="new york" occupation="student"></person>')
,('One country','<country name="Germany" capital="Berlin" continent="Europe"></country>');
--this query relies on all possible attributes known in advance.
--common attributes, like the name, are returned for a person and for a country
--differing attributes return as NULL.
--One advantage might be, that you can use a specific datatype if appropriate.
SELECT t.ID
,t.Descr
,t.VAL.value('(/*[1]/#name)[1]','nvarchar(max)') AS [name]
,t.VAL.value('(/*[1]/#age)[1]','nvarchar(max)') AS [age]
,t.VAL.value('(/*[1]/#city)[1]','nvarchar(max)') AS [city]
,t.VAL.value('(/*[1]/#occupation)[1]','nvarchar(max)') AS [occupation]
,t.VAL.value('(/*[1]/#city)[1]','nvarchar(max)') AS [city]
,t.VAL.value('(/*[1]/#capital)[1]','nvarchar(max)') AS [capital]
,t.VAL.value('(/*[1]/#continent)[1]','nvarchar(max)') AS [continent]
FROM #tbl t;
--This query returns as classical EAV (entity-attribute-value) list
--In this result you get each attribute on its own line
SELECT t.ID
,t.Descr
,A.attrs.value('local-name(.)','nvarchar(max)') AS AttrName
,A.attrs.value('.','nvarchar(max)') AS AttrValue
FROM #tbl t
CROSS APPLY t.VAL.nodes('/*[1]/#*') A(attrs);
Both approaches might be generated as a statement on string-level and then executed by EXEC() or sp_executesql.
Hint: One approach might be to insert the EAV list into a tolerant staging table and proceed from there with conditional aggregation, PIVOT or hardcoded VIEWs.
Dynamic approach
In order to read the <person> elements we would need this:
SELECT t.ID
,t.Descr
,t.VAL.value('(/*[1]/#name)[1]','nvarchar(max)') AS [name]
,t.VAL.value('(/*[1]/#age)[1]','nvarchar(max)') AS [age]
,t.VAL.value('(/*[1]/#city)[1]','nvarchar(max)') AS [city]
,t.VAL.value('(/*[1]/#occupation)[1]','nvarchar(max)') AS [occupation]
FROM #tbl t
WHERE VAL.value('local-name(/*[1])','varchar(100)')='person';
All we have to do is to generate the changing part:
Try this:
A new mockup with a real table
CREATE TABLE SimulateYourTable(ID INT IDENTITY, Descr VARCHAR(100), VAL XML);
INSERT INTO SimulateYourTable VALUES
('One person',N'|<person name="bob" age="22" city="new york" occupation="student"></person>')
,('One more person','<person name="bob" age="22" city="new york" occupation="student"></person>')
,('One country','<country name="Germany" capital="Berlin" continent="Europe"></country>');
--Filter for <person> entities
DECLARE #entityName NVARCHAR(100)='person';
--This is a string representing the command
DECLARE #cmd NVARCHAR(MAX)=
'SELECT t.ID
,t.Descr
***columns here***
FROM SimulateYourTable t
WHERE VAL.value(''local-name(/*[1])'',''varchar(100)'')=''***name here***''';
--with this we can create all the columns
--Hint: With SQL Server 2017+ there is STRING_AGG() - much simpler!
DECLARE #columns NVARCHAR(MAX)=
(
SELECT CONCAT(',t.VAL.value(''(/*[1]/#',Attrib.[name],')[1]'',''nvarchar(max)'') AS ',QUOTENAME(Attrib.[name]))
FROM SimulateYourTable t
CROSS APPLY t.VAL.nodes('//#*') AllAttrs(a)
CROSS APPLY (SELECT a.value('local-name(.)','varchar(max)')) Attrib([name])
WHERE VAL.value('local-name(/*[1])','varchar(100)')=#entityName
GROUP BY Attrib.[name]
FOR XML PATH(''),TYPE
).value('.','nvarchar(max)');
--Now we stuff this into our command
SET #cmd=REPLACE(#cmd,'***columns here***',#columns);
SET #cmd=REPLACE(#cmd,'***name here***',#entityName);
--This is the command.
--Hint: You might use this to create physical VIEWs without the need to type them in...
PRINT #cmd;
You can use EXEC(#cmd) to execute this dynamic SQL and check the result.