Estou tentando obter uma estimativa aproximada (de ordem de grandeza) de quanto tempo a consulta a seguir pode levar:

mysql> EXPLAIN SELECT t1.col1, t1_col4 FROM t1 LEFT JOIN t2 ON t1.col1=t2.col1 WHERE col2=0 AND col3 IS NULL;
+----+-------------+--------------------+------+---------------+------------+---------+-----------------------------+---------+--------------------------+
| id | select_type | table              | type | possible_keys | key        | key_len | ref                         | rows    | Extra                    |
+----+-------------+--------------------+------+---------------+------------+---------+-----------------------------+---------+--------------------------+
|  1 | SIMPLE      | t1                 | ref  | foobar        | foobar     | 4       | const                       | 9715129 |                          | 
|  1 | SIMPLE      | t2                 | ref  | col1          | col1       | 4       | db2.t1.col1                 |   42318 | Using where; Using index | 
+----+-------------+--------------------+------+---------------+------------+---------+-----------------------------+---------+--------------------------+
2 rows in set (0.00 sec)

mysql>