Use a LIKE statement on SQL Server XML Datatype

Question

If you have a varchar field you can easily do SELECT * FROM TABLE WHERE ColumnA LIKE '%Test%' to see if that column contains a certain string.

How do you do that for XML Type?

I have the following which returns only rows that have a 'Text' node but I need to search within that node

select * from WebPageContent where data.exist('/PageContent/Text') = 1

Solution 1

You should be able to do this quite easily:

SELECT * 
FROM WebPageContent 
WHERE data.value('(/PageContent/Text)[1]', 'varchar(100)') LIKE 'XYZ%'

The .value method gives you the actual value, and you can define that to be returned as a VARCHAR(), which you can then check with a LIKE statement.

Mind you, this isn't going to be awfully fast. So if you have certain fields in your XML that you need to inspect a lot, you could:

• create a stored function which gets the XML and returns the value you're looking for as a VARCHAR()
• define a new computed field on your table which calls this function, and make it a PERSISTED column

With this, you'd basically "extract" a certain portion of the XML into a computed field, make it persisted, and then you can search very efficiently on it (heck: you can even INDEX that field!).

Marc

Solution 2

Yet another option is to cast the XML as nvarchar, and then search for the given string as if the XML vas a nvarchar field.

SELECT * 
FROM Table
WHERE CAST(Column as nvarchar(max)) LIKE '%TEST%'

I love this solution as it is clean, easy to remember, hard to mess up, and can be used as a part of a where clause.

This might not be the best performing solution, so think twice before deplying it to production. It is however very usefull for a quick debug session, which is where I mostly use it.

EDIT: As Cliff mentions it, you could use:

...nvarchar if there's characters that don't convert to varchar

Solution 3

Another option is to search the XML as a string by converting it to a string and then using LIKE. However as a computed column can't be part of a WHERE clause you need to wrap it in another SELECT like this:

SELECT * FROM
    (SELECT *, CONVERT(varchar(MAX), [COLUMNA]) as [XMLDataString] FROM TABLE) x
WHERE [XMLDataString] like '%Test%'

Comments

[Jon]

I'm basically implemeting a search feature so I want to search the XML column only on the 'Text' nodes and then return a substring to indicate that the search has found a match. For example search on 'hi there' instead of returning the whole xml column I'd just return a substring such as 'the chap said hi there and carried...'

[RickNZ]

Beat me to it by 5 seconds. Another possibility is to consider using free text search, if your data is amenable...

[Jon]

Do I need parameters to prevent injection somehow?

[marc_s]

BE AWARE: those XML function ARE case-sensitive - DATA.VALUE will not work ! It needs be to .value(...)

[jhilden]

to search the whole filed: WHERE xmlField.value('.', 'varchar(max)') LIKE '%FOO%'

[Cliff Coulter]

Ditto on that, or nvarchar if there's characters that don't convert to varchar SELECT * FROM Table WHERE CAST(Column as nvarchar(max)) LIKE '%TEST%'

[digz6666]

[Err] 42000 - [SQL Server]Conversion of one or more characters from XML to target collation impossible

[digz6666]

[Err] 22018 - [SQL Server]Explicit conversion from data type xml to text is not allowed.

[Squazz]

Sounds like you are doing something wrong @digz6666

[Squazz]

@digz6666 have you tried nvarchar instead of just varchar?

[Squazz]

@digz6666 if possible, remove your downvote then? ;)

[digz6666]

@Squazz You last voted on this answer yesterday. Your vote is now locked in unless this answer is edited. :)

[aruno]

watch out for pesky Xml namespaces if you get NULL back

[Rudy Hinojosa]

Be advised this may bypass any selective xml indexes you may have in place and take a hit on performance.