Deleting mismatches - which is more optimal?
I have tables that should be 1:1 relations but occasionally, they become mismatched, one table having more records than the other. I have been wondering which is the most optimal way to delete things like this.

I have a delete using a join (item_id is primary key):

mysql> delete from items_keys using items_keys left join items using (item_id) where items.item_id is NULL;

vs. using a subquery:

mysql> delete from items_keys where item_id not in (select item_id from items);

Sometimes, the 2nd seems faster, but using a join seems more orthodox to me. I'm curious what people think about this.

If I make these into select queries (instead of delete) and run explain, I get:

mysql> explain select count(*) from items_keys left join items using (item_id) where items.item_id is NULL;+----+-------------+------------+--------+---------------+---------+---------+--------------------------+-------+--------------------------------------+
| id | select_type | table      | type   | possible_keys | key     | key_len | ref                      | rows  | Extra                                |
+----+-------------+------------+--------+---------------+---------+---------+--------------------------+-------+--------------------------------------+
|  1 | SIMPLE      | items_keys | index  | NULL          | PRIMARY | 8       | NULL                     | 73915 | Using index                          | 
|  1 | SIMPLE      | items      | eq_ref | PRIMARY       | PRIMARY | 8       | grazr.items_keys.item_id |     1 | Using where; Using index; Not exists | 
+----+-------------+------------+--------+---------------+---------+---------+--------------------------+-------+--------------------------------------+
2 rows in set (0.03 sec)

mysql> explain select count(*) from items_keys where item_id not in (select item_id from items);
+----+--------------------+------------+-----------------+---------------+---------+---------+------+-------+--------------------------+
| id | select_type        | table      | type            | possible_keys | key     | key_len | ref  | rows  | Extra                    |
+----+--------------------+------------+-----------------+---------------+---------+---------+------+-------+--------------------------+
|  1 | PRIMARY            | items_keys | index           | NULL          | PRIMARY | 8       | NULL | 73918 | Using where; Using index | 
|  2 | DEPENDENT SUBQUERY | items      | unique_subquery | PRIMARY       | PRIMARY | 8       | func |     1 | Using index              | 
+----+--------------------+------------+-----------------+---------------+---------+---------+------+-------+--------------------------+
2 rows in set (0.01 sec)

'rows' is about the same. Index usage appears similar. Though using a subquery seems like it could be more expensive. Maybe this is a simple question I'm asking.