1 row in set (0.00 sec)
The NULL value in the key column of the EXPLAIN output tell us that MySQL won't be using an index for this query. In fact, the NULL value in the possible_keys column tells us that there were no indexes to pick from at all. If this type of query is likely to be common, we can simply add an index and rerun the query (or the EXPLAIN) to verify that MySQL uses it.