我有这个sql查询在MySQL 5.1非规范化表上运行。它按照我想要的方式工作,但速度可能很慢。我在日期栏中添加了一个索引,但它仍然需要更快。有关如何更快获得此建议的任何建议? (也许有参加呢?)使用算术运算优化MySQL嵌套选择
SELECT DISTINCT(bucket) AS b,
(possible_free_slots -
(SELECT COUNT(availability)
FROM ip_bucket_list
WHERE bucket = b
AND availability = 'used'
AND tday = 'evening'
AND day LIKE '2012-12-14%'
AND network = '10_83_mh1_bucket')) AS free_slots
FROM ip_bucket_list
ORDER BY free_slots DESC;
各个查询速度快:
SELECT DISTINCT(bucket) FROM ip_bucket_list;
1024 rows in set (0.05 sec)
SELECT COUNT(availability) from ip_bucket_list WHERE bucket = 0 AND availability = 'used' AND tday = 'evening' AND day LIKE '2012-12-14%' AND network = '10_83_mh1_bucket';
1 row in set (0.00 sec)
表:
mysql> describe ip_bucket_list;
+---------------------+--------------+------+-----+-------------------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------------------+--------------+------+-----+-------------------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| ip | varchar(50) | YES | | NULL | |
| bucket | int(11) | NO | MUL | NULL | |
| availability | varchar(20) | YES | | NULL | |
| network | varchar(100) | NO | MUL | NULL | |
| possible_free_slots | int(11) | NO | | NULL | |
| tday | varchar(20) | YES | | NULL | |
| day | timestamp | NO | MUL | CURRENT_TIMESTAMP | |
+---------------------+--------------+------+-----+-------------------+----------------+
和DESC:
DESC SELECT DISTINCT(bucket) as b,(possible_free_slots - (SELECT COUNT(availability) from ip_bucket_list WHERE bucket = b AND availability = 'used' AND tday = 'evening' AND day LIKE '2012-12-14%' AND network = '10_83_mh1_bucket')) as free_slots FROM ip_bucket_list ORDER BY free_slots DESC;
+----+--------------------+----------------+------+-----------------------------------------+--------+---------+------+--------+---------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+--------------------+----------------+------+-----------------------------------------+--------+---------+------+--------+---------------------------------+
| 1 | PRIMARY | ip_bucket_list | ALL | NULL | NULL | NULL | NULL | 328354 | Using temporary; Using filesort |
| 2 | DEPENDENT SUBQUERY | ip_bucket_list | ref | bucket,network,ip_bucket_list_day_index | bucket | 4 | func | 161 | Using where |
+----+--------------------+----------------+------+-----------------------------------------+--------+---------+------+--------+---------------------------------+
你可以张贴一些示例行和预期的输出?这可能有帮助。 –