Using mySQL subqueries for selective deleting

gistfile1.txt

mysql> select entity_id, language from field_data_body where entity_id = 9311;
+-----------+----------+
| entity_id | language |
+-----------+----------+
|      9311 | en       |
|      9311 | und      |
+-----------+----------+
2 rows in set (0.00 sec)
# I need to delete only those entries with language 'und'
# See which nodes
mysql> select entity_id, language from field_data_body where language = 'und' AND entity_id IN (SELECT entity_id from  field_data_body where language='en');

...

|      8798 | und      |
|      9029 | und      |
|      9030 | und      |
|      9311 | und      |
+-----------+----------+
156 rows in set (0.05 sec)
# Now, delete them using a subquery
# x is an alias for the temp table produced for the subquery.

mysql> DELETE from field_data_body WHERE language='und' AND entity_id IN (SELECT entity_id from (SELECT entity_id from field_data_body where language ='en') x);


Note: The following won't work:
DELETE from field_data_body WHERE language='und' AND entity_id IN (SELECT entity_id from field_data_body where language ='en);