title: How to estimate SQL query timing?
body: <p>I'm trying to get an rough (order-of-magnitude) estimate of how long time the following query could take:</p>
  
  <pre><code>mysql&gt; 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&gt; 
  </code></pre>