有没有办法进一步优化这个操作,或者我应该对需要 9 秒来计算 1100 万行感到满意?
devuser@xcmst > mysql --user=user --password=pass -D marctoxctransformation -e "desc record_updates"
+--------------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------+----------+------+-----+---------+-------+
| record_id | int(11) | YES | MUL | NULL | |
| date_updated | datetime | YES | MUL | NULL | |
+--------------+----------+------+-----+---------+-------+
devuser@xcmst > date; mysql --user=user --password=pass -D marctoxctransformation -e "select count(*) from record_updates where date_updated > '2009-10-11 15:33:22' "; date
Thu Dec 9 11:13:17 EST 2010
+----------+
| count(*) |
+----------+
| 11772117 |
+----------+
Thu Dec 9 11:13:26 EST 2010
devuser@xcmst > mysql --user=user --password=pass -D marctoxctransformation -e "explain select count(*) from record_updates where date_updated > '2009-10-11 15:33:22' "
+----+-------------+----------------+-------+--------------------------------------------------------+--------------------------------------------------------+---------+------+----------+--------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+----------------+-------+--------------------------------------------------------+--------------------------------------------------------+---------+------+----------+--------------------------+
| 1 | SIMPLE | record_updates | index | idx_marctoxctransformation_record_updates_date_updated | idx_marctoxctransformation_record_updates_date_updated | 9 | NULL | 11772117 | Using where; Using index |
+----+-------------+----------------+-------+--------------------------------------------------------+--------------------------------------------------------+---------+------+----------+--------------------------+
devuser@xcmst > mysql --user=user --password=pass -D marctoxctransformation -e "show keys from record_updates"
+----------------+------------+--------------------------------------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+----------------+------------+--------------------------------------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+
| record_updates | 1 | idx_marctoxctransformation_record_updates_date_updated | 1 | date_updated | A | 2416 | NULL | NULL | YES | BTREE | |
| record_updates | 1 | idx_marctoxctransformation_record_updates_record_id | 1 | record_id | A | 11772117 | NULL | NULL | YES | BTREE | |
+----------------+------------+--------------------------------------------------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+