SQL 中的 XML 数据类型列

Question

I have a table called assessments. In that table, we are storing responses to a list of questions from the application and we have an XML column with an XML data type that stores the same responses for the questions in the XML format. Mostly the XML column will have a null value when the user is refused to pass it. Can anyone know how much storage it will take for the XML column if the values are passed and not passed?.

Answer 1

The internal representation of an XML document is not what you see when looking at the XML document.

Here is a good link on the subject: Where to find the size of SQL Server data types?

For example, contrary to popular belief, XML is smaller than JSON.

SQL

DECLARE @tbl TABLE (ID INT IDENTITY PRIMARY KEY, jsondata NVARCHAR(MAX), xmldata XML);
INSERT INTO @tbl (jsondata, xmldata)
VALUES
(N'{
    "SquidGame": {
        "Genre": "Thriller",
        "Rating": {
            "@Type": "Imdb",
            "#text": "8.1"
        },
        "Stars": [
            "Lee Jung-jae",
            "Park Hae-soo"
        ],
        "Budget": null
    }
}', N'<SquidGame>
      <Genre>Thriller</Genre>
      <Rating Type="Imdb">8.1</Rating>
      <Stars>Lee Jung-jae</Stars>
      <Stars>Park Hae-soo</Stars>
      <Budget />
    </SquidGame>');

SELECT * 
    , jsondata_length = DATALENGTH(jsondata), xmldata_length = DATALENGTH(xmldata)
FROM @tbl;

Output

+----+-----------------+----------------+
| ID | jsondata_length | xmldata_length |
+----+-----------------+----------------+
|  1 |             374 |            220 |
+----+-----------------+----------------+