[英]Refuses to use index on TIMESTAMP field
我不明白為什么在一個字段上的相同查詢使用索引,而在另一個字段上卻不使用索引。 這兩個字段都有索引。 一個字段是INT,另一個字段是TIMESTAMP。 某種魔術。 救命!
這是表:
CREATE TABLE `fb_posts` (
`postID` BIGINT(20) NOT NULL AUTO_INCREMENT,
`url` VARCHAR(255) NOT NULL,
`time` INT(11) NOT NULL,
`partnerID` INT(11) NOT NULL,
`aTime` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (`postID`),
INDEX `time` (`time`),
INDEX `aTime` (`aTime`)
)
COLLATE='utf8_general_ci'
ENGINE=InnoDB
ROW_FORMAT=COMPRESSED
AUTO_INCREMENT=67640377;
說明查詢:
1。
mysql> explain SELECT
-> `fb_posts`.`partnerID`
-> FROM
-> `fb_posts`
-> WHERE
-> `fb_posts`.`time` > 1551107400
-> AND `fb_posts`.`time` <= 1551108000
->
-> ;
+----+-------------+----------+-------+---------------+------+---------+------+------+-----------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+----------+-------+---------------+------+---------+------+------+-----------------------+
| 1 | SIMPLE | fb_posts | range | time | time | 4 | NULL | 1 | Using index condition |
+----+-------------+----------+-------+---------------+------+---------+------+------+-----------------------+
1 row in set (0.00 sec)
2。
mysql> explain SELECT
-> `fb_posts`.`partnerID`
-> FROM
-> `fb_posts`
-> WHERE
-> `fb_posts`.`aTime` > 1551107400
-> AND `fb_posts`.`aTime` <= 1551108000
-> ;
+----+-------------+----------+------+---------------+------+---------+------+----------+-------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+----------+------+---------------+------+---------+------+----------+-------------+
| 1 | SIMPLE | fb_posts | ALL | aTime | NULL | NULL | NULL | 69567867 | Using where |
+----+-------------+----------+------+---------------+------+---------+------+----------+-------------+
1 row in set, 4 warnings (0.00 sec)
為什么???
優化器創建方式。 他們使用統計信息來找出哪種方式最適合此查詢。
嘗試此操作以查看統計信息並閱讀手冊“ PROCEDURE ANALYSE()”
SELECT * FROM `fb_posts` PROCEDURE ANALYSE();
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