explain select SQL_NO_CACHE  lots.productId, MAX(lots.tsExpires)          FROM lots  WHERE productID in(60195,60199)  GROUP BY productId;  

+------+-------------+-------+-------+---------------------------+----------+---------+------+------+---------------------------------------+

| id   | select_type | table | type  | possible_keys             | key      | key_len | ref  | rows | Extra                                 |

+------+-------------+-------+-------+---------------------------+----------+---------+------+------+---------------------------------------+

|    1 | SIMPLE      | lots  | range | productId,prodId,idx_sky1 | idx_sky1 | 4       | NULL |    1 | Using where; Using index for group-by |

+------+-------------+-------+-------+---------------------------+----------+---------+------+------+---------------------------------------+

1 row in set (6,91 sec)

mysql> explain select SQL_NO_CACHE DISTINCT  lots.productId, MAX(lots.tsExpires) FROM lots  WHERE productID in(60195,60199)  GROUP BY productId;

+------+-------------+-------+-------+---------------------------+-----------+---------+------+------+--------------------------+

| id   | select_type | table | type  | possible_keys             | key       | key_len | ref  | rows | Extra                    |

+------+-------------+-------+-------+---------------------------+-----------+---------+------+------+--------------------------+

|    1 | SIMPLE      | lots  | range | productId,prodId,idx_sky1 | productId | 4       | NULL |    2 | Using where; Using index |

+------+-------------+-------+-------+---------------------------+-----------+---------+------+------+--------------------------+

1 row in set (0,04 sec)

| productId              | int(11) unsigned                    | NO   | MUL | NULL         

| tsExpires              | timestamp                           | NO   | MUL | 0000-00-00 00:00:00 |