How to insert an attribute into xml data which is saved as nvarchar(max)

Question

Let's say there is the following XML data and I want to add an attribute into salary like currency="INR" :

<employee>
    <salary amount="6000"/>
</employee>

1. If this data is stored in a column of type XML , then another attribute is being added easily just by using this code snippet:

    UPDATE TABLENAME SET COLUMNNAME.modify('insert attribute currency{"INR"} into (/employee/salary)[1]') 

2. and if this data is stored in a column of type nvarchar(max) , then the following query is not working even after casting the data as xml :

    UPDATE TABLENAME SET CAST(CAST(COLUMNNAME AS VARCHAR(MAX)) AS XML).modify('insert attribute currency{"INR"} into (/employee/salary)[1]') 

So, help me to resolve second point as I have a column as nvarchar and I need to insert an attribute into saved xml data.

Answer 1

modify() Method works only with variable/column directly and can only used in the SET clause.

So, to solve this since you are storing your data as NVARCHAR , you have two choices:

1. Alter your table and add a new column with XML datatype, move the data to it from your column, and then UPDATE the data using modify()

2. Create/declare a table to store your data as XML and do the UPDATE .

Here is an example for what you provide:

CREATE TABLE T
(
  Value NVARCHAR(MAX)
);

INSERT INTO T
SELECT N'<employee>
           <salary amount="6000"/>
         </employee>';

DECLARE @V XML;

SELECT @V = CAST(Value AS XML)
FROM T;

SET @V.modify('insert attribute currency{"INR"} into (/employee/salary)[1]');

UPDATE T
SET Value = CAST(@V AS NVARCHAR(MAX));

SELECT * FROM T;

Live demo