SQL REPLACE function inside Xml.modify 'replace value of' - sql-server

Question

I'm trying to update some XML data in SQL Server. The XML contains data that looks like this:
<root>
<id>1</id>
<timestamp>16-10-2017 19:24:55</timestamp>
</root>
Let's say this XML exists in a column called Data in a table called TestTable.
I would like to be able to change the hyphens in the timestamp to forward slashes.
I was hoping I might be able to do something like:
update TestTable
set Data.modify('replace value of
(/root/timestamp/text())[1] with REPLACE((/root/timestamp/text())[1], "-", "/")')
I get the following error:
XQuery [TestTable]: There is no function '{http://www.w3.org/2004/07/xpath-functions}:REPLACE()'
When I think about it, this makes sense. But I wonder, is there a way to do this in a single update statement? Or do I first need to query the timestamp value and save it as a variable, and then update the XML with the variable?

Answer 1

You can also do this with a join to an inline view and use the SQL REPLACE function:
CREATE TABLE TestTable
(
Id INT IDENTITY(1,1) NOT NULL,
Data XML NOT NULL
)
INSERT TestTable (Data) VALUES ('<root>
<id>1</id>
<timestamp>16-10-2017 19:24:55</timestamp>
</root>')
UPDATE TestTable
SET Data.modify('replace value of
(/root/timestamp/text())[1] with sql:column("T2.NewData")')
FROM TestTable T1
INNER JOIN (
SELECT Id
, REPLACE( Data.value('(/root/timestamp/text())[1]', 'nvarchar(max)'), '-', '/') AS NewData
FROM TestTable
) T2
ON T1.Id = T2.Id
SELECT * FROM TestTable

Answer 2

Note: this answer assumes you want to have this formatted for the purpose of displaying this as a string, and not parsing the content as a xs:dateTime. If you want the latter, Shungo's answer will format it as such.
It seems that replace is not a supported XQuery function in SQL Server at the time of this writing. You can use the substring function along with the concat function in a "replace value of (XML DML)" though.
CREATE TABLE #t(x XML);
INSERT INTO #t(x)VALUES(N'<root><id>1</id><timestamp>16-10-2017 19:24:55</timestamp></root>');
UPDATE
#t
SET
x.modify('replace value of (/root/timestamp/text())[1]
with concat(substring((/root/timestamp/text())[1],1,2),
"/",
substring((/root/timestamp/text())[1],4,2),
"/",
substring((/root/timestamp/text())[1],7)
) ')
SELECT*FROM #t;
Giving as a result:
<root><id>1</id><timestamp>16/10/2017 19:24:55</timestamp></root>

Answer 3

If there's no external need you have to fullfill, you should use ISO8601 date/time strings within XML.
Your dateTime-string is culture related. Reading this on different systems with differing language or dateformat settings will lead to errors or - even worse!!! - to wrong results.
A date like "08-10-2017" can be the 8th of October or the 10th of August...
The worst point is, that this might pass all your tests successfully, but will break on a customer's machine with strange error messages or bad results down to real data dammage!
Switching the hyphens to slashes is just cosmetic! An XML is a strictly defined data container. Any non-string data must be represented as a secure convertible string.
This is what you should do:
DECLARE #tbl TABLE(ID INT IDENTITY,YourXML XML);
INSERT INTO #tbl VALUES
(N'<root>
<id>1</id>
<timestamp>16-10-2017 19:24:55</timestamp>
</root>');
UPDATE #tbl SET YourXml.modify(N'replace value of (/root/timestamp/text())[1]
with concat( substring((/root/timestamp/text())[1],7,4), "-"
,substring((/root/timestamp/text())[1],4,2), "-"
,substring((/root/timestamp/text())[1],1,2), "T"
,substring((/root/timestamp/text())[1],12,8)
) cast as xs:dateTime?');
SELECT * FROM #tbl;
The result
<root>
<id>1</id>
<timestamp>2017-10-16T19:24:55</timestamp>
</root>

Answer 4

you can try string replacement like below
update testtable
set data= cast(
concat(
left(cast(data as varchar(max)),charindex('<timestamp>',cast(data as varchar(max)))+len('<timestamp>')-1),
replace(
substring(
cast(data as varchar(max)),
len('<timestamp>') +
charindex( '<timestamp>', cast(data as varchar(max))) ,
charindex('</timestamp>',cast(data as varchar(max)))
-charindex('<timestamp>',cast(data as varchar(max)))
-len('<timestamp>')
),
'-','/'),
right(cast(data as varchar(max)),len(cast(data as varchar(max)))-charindex('</timestamp>',cast(data as varchar(max)))+1)
) as xml)
select *
from testtable
working demo