If the only thing you are storing in the database is the XML data, what is to stop you from storing the file directly on the filesystem and bypassing the overhead of querying the database for the single field?
If backups are your concern, there are methods to backup a directory as well.
Usage of MySQL (or other RDBMS) implies there is a relational aspect to the data you are storing. If there's no relationship, this is probably not the tool you are looking for.
You could try using MySQL's mysqldump utility.
There is an option to make mysqldump export in XML
[redwards@lw-lts-155 ~]$ mysqldump --help | grep xml
-X, --xml Dump a database as well formed XML.
In your case, you could dump the table mydb.mytable like this:
mysqldump --xml mydb mytable > mytable.xml
EXAMPLE
For the given table
mysql> show create table groupby\G
*************************** 1. row ***************************
Table: groupby
Create Table: CREATE TABLE `groupby` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`num` int(11) DEFAULT NULL,
PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=17 DEFAULT CHARSET=latin1
1 row in set (0.01 sec)
mysql> select * from groupby;
+----+------------+
| id | num |
+----+------------+
| 1 | 360370418 |
| 2 | 429187192 |
| 3 | 1064824747 |
| 4 | 1328623077 |
| 5 | 740702064 |
| 6 | 1071610692 |
| 7 | 428008187 |
| 8 | 279178462 |
| 9 | 360370418 |
| 10 | 429187192 |
| 11 | 1064824747 |
| 12 | 1328623077 |
| 13 | 740702064 |
| 14 | 1071610692 |
| 15 | 428008187 |
| 16 | 279178462 |
+----+------------+
16 rows in set (0.00 sec)
mysql>
just mysqldump to a textfile.
Here is what the XML actually looks like
<?xml version="1.0"?>
<mysqldump xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<database name="eggyal">
<table_structure name="groupby">
<field Field="id" Type="int(11)" Null="NO" Key="PRI" Extra="auto_increment" Comment="" />
<field Field="num" Type="int(11)" Null="YES" Key="" Extra="" Comment="" />
<key Table="groupby" Non_unique="0" Key_name="PRIMARY" Seq_in_index="1" Column_name="id" Collation="A" Cardinality="16" Null="" Index_type="BTREE" Comment="" Index_comment="" />
<options Name="groupby" Engine="MyISAM" Version="10" Row_format="Fixed" Rows="16" Avg_row_length="9" Data_length="144" Max_data_length="2533274790395903" Index_length="2048" Data_free="0" Auto_increment="17" Create_time="2012-11-26 22:39:22" Update_time="2012-11-26 22:39:22" Collation="latin1_swedish_ci" Create_options="" Comment="" />
</table_structure>
<table_data name="groupby">
<row>
<field name="id">1</field>
<field name="num">360370418</field>
</row>
<row>
<field name="id">2</field>
<field name="num">429187192</field>
</row>
<row>
<field name="id">3</field>
<field name="num">1064824747</field>
</row>
<row>
<field name="id">4</field>
<field name="num">1328623077</field>
</row>
<row>
<field name="id">5</field>
<field name="num">740702064</field>
</row>
<row>
<field name="id">6</field>
<field name="num">1071610692</field>
</row>
<row>
<field name="id">7</field>
<field name="num">428008187</field>
</row>
<row>
<field name="id">8</field>
<field name="num">279178462</field>
</row>
<row>
<field name="id">9</field>
<field name="num">360370418</field>
</row>
<row>
<field name="id">10</field>
<field name="num">429187192</field>
</row>
<row>
<field name="id">11</field>
<field name="num">1064824747</field>
</row>
<row>
<field name="id">12</field>
<field name="num">1328623077</field>
</row>
<row>
<field name="id">13</field>
<field name="num">740702064</field>
</row>
<row>
<field name="id">14</field>
<field name="num">1071610692</field>
</row>
<row>
<field name="id">15</field>
<field name="num">428008187</field>
</row>
<row>
<field name="id">16</field>
<field name="num">279178462</field>
</row>
</table_data>
</database>
</mysqldump>
As for the DTD itself, you should look around StackOverflow and ServerFault
You could also XML dump just the structure using --no-data option
mysqldump --xml --no-data mydb mytable > mytable.xml
which produces
<?xml version="1.0"?>
<mysqldump xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<database name="eggyal">
<table_structure name="groupby">
<field Field="id" Type="int(11)" Null="NO" Key="PRI" Extra="auto_increment" Comment="" />
<field Field="num" Type="int(11)" Null="YES" Key="" Extra="" Comment="" />
<key Table="groupby" Non_unique="0" Key_name="PRIMARY" Seq_in_index="1" Column_name="id" Collation="A" Cardinality="16" Null="" Index_type="BTREE" Comment="" Index_comment="" />
<options Name="groupby" Engine="MyISAM" Version="10" Row_format="Fixed" Rows="16" Avg_row_length="9" Data_length="144" Max_data_length="2533274790395903" Index_length="2048" Data_free="0" Auto_increment="17" Create_time="2012-11-26 22:39:22" Update_time="2012-11-26 22:39:22" Collation="latin1_swedish_ci" Create_options="" Comment="" />
</table_structure>
</database>
</mysqldump>
Take that output and scult it into a DTD
Best Answer
For MySQL, you might use use the ExtractData function.
If you are also using Windows (it needs Net Framework) then this old and outdated tool might still do the job.
http://xmltodb.sourceforge.net/
I have used it in the past and it converts the XML file to plain INSERT commands. For simple XML files it actually works. Of course the INSERT commmands will need some tweaking (change " or ') according to the db flavor but 90% of the actual job is done with the tool.
Commercial tools like XMLSpy http://www.altova.com/xmlspy/database-xml.html have a similar functionality (you may try the trial editions).
You can even try importing the file to MS Excel and then export to CSV for importing into the MySQL database. MS Excel has a nice feature XML maps that can map XML attributes and entities to columns. I tested it and it will easily work with a well formatted XML like yours.