所以,我从来没有理解过MySQL的解释.我理解粗略的概念,即您应该在possible_keys
列中至少有一个条目才能使用索引,而且简单的查询更好.但是ref和eq_ref有什么不同呢?优化查询的最佳方式是什么?
例如,这是我的最新查询,我正在试图弄清楚为什么要花很长时间(从django
个型号生成):
+----+-------------+---------------------+--------+-----------------------------------------------------------+---------------------------------+---------+--------------------------------------+------+---------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+---------------------+--------+-----------------------------------------------------------+---------------------------------+---------+--------------------------------------+------+---------------------------------+
| 1 | SIMPLE | T6 | ref | yourock_achiever_achievement_id,yourock_achiever_alias_id | yourock_achiever_alias_id | 4 | const | 244 | Using temporary; Using filesort |
| 1 | SIMPLE | T5 | eq_ref | PRIMARY | PRIMARY | 4 | paul.T6.achievement_id | 1 | Using index |
| 1 | SIMPLE | T4 | ref | yourock_achiever_achievement_id,yourock_achiever_alias_id | yourock_achiever_achievement_id | 4 | paul.T6.achievement_id | 298 | |
| 1 | SIMPLE | yourock_alias | eq_ref | PRIMARY | PRIMARY | 4 | paul.T4.alias_id | 1 | Using index |
| 1 | SIMPLE | yourock_achiever | ref | yourock_achiever_achievement_id,yourock_achiever_alias_id | yourock_achiever_alias_id | 4 | paul.T4.alias_id | 152 | |
| 1 | SIMPLE | yourock_achievement | eq_ref | PRIMARY | PRIMARY | 4 | paul.yourock_achiever.achievement_id | 1 | |
+----+-------------+---------------------+--------+-----------------------------------------------------------+---------------------------------+---------+--------------------------------------+------+---------------------------------+
6 rows in set (0.00 sec)
我曾希望对MySQL有足够的了解,并解释说不需要查询.唉,您似乎无法从EXPLAIN语句中获得足够的信息,您需要原始SQL.查询:
SELECT `yourock_achievement`.`id`,
`yourock_achievement`.`modified`,
`yourock_achievement`.`created`,
`yourock_achievement`.`string_id`,
`yourock_achievement`.`owner_id`,
`yourock_achievement`.`name`,
`yourock_achievement`.`description`,
`yourock_achievement`.`owner_points`,
`yourock_achievement`.`url`,
`yourock_achievement`.`remote_image`,
`yourock_achievement`.`image`,
`yourock_achievement`.`parent_achievement_id`,
`yourock_achievement`.`slug`,
`yourock_achievement`.`true_points`
FROM `yourock_achievement`
INNER JOIN
`yourock_achiever`
ON `yourock_achievement`.`id` = `yourock_achiever`.`achievement_id`
INNER JOIN
`yourock_alias`
ON `yourock_achiever`.`alias_id` = `yourock_alias`.`id`
INNER JOIN
`yourock_achiever` T4
ON `yourock_alias`.`id` = T4.`alias_id`
INNER JOIN
`yourock_achievement` T5
ON T4.`achievement_id` = T5.`id`
INNER JOIN
`yourock_achiever` T6
ON T5.`id` = T6.`achievement_id`
WHERE
T6.`alias_id` = 6
ORDER BY
`yourock_achievement`.`modified` DESC