Mysql 使用唯一索引对行为进行匹配
向多表全文布尔搜索添加唯一键时,结果会在3种任意状态中的1种循环,只有1种是正确的 在检查下面的sqlfiddle时请记住这一点,因为查询最初可能会正常工作——在这种情况下,在左侧面板中添加空格,然后重新生成并重新运行——然后它应该被破坏(但这是非常容易出错的) 以下是有疑问的问题:Mysql 使用唯一索引对行为进行匹配,mysql,full-text-search,innodb,unique-index,sqlfiddle,Mysql,Full Text Search,Innodb,Unique Index,Sqlfiddle,向多表全文布尔搜索添加唯一键时,结果会在3种任意状态中的1种循环,只有1种是正确的 在检查下面的sqlfiddle时请记住这一点,因为查询最初可能会正常工作——在这种情况下,在左侧面板中添加空格,然后重新生成并重新运行——然后它应该被破坏(但这是非常容易出错的) 以下是有疑问的问题: SELECT `i`.`item_id`, `g_a`.`alias` AS `group`, `i`.`name` AS `name` FROM `item` `i` JOIN `group_alias
SELECT `i`.`item_id`, `g_a`.`alias` AS `group`, `i`.`name` AS `name`
FROM `item` `i`
JOIN `group_alias` `g_a` USING (group_id)
WHERE
MATCH (`g_a`.`alias`) AGAINST ('Mac*' IN BOOLEAN MODE)
OR
MATCH (`i`.`name`) AGAINST ('Mac*' IN BOOLEAN MODE);
很简单。但添加了以下独特的索引:
ALTER TABLE `item_with_unique` ADD UNIQUE INDEX `unique_item_group` (`group_id`, `name`)
结果在这三种状态之间任意循环:
CREATE TABLE `group` (
`group_id` INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
`name` VARCHAR(256),
FULLTEXT INDEX `search` (`name`)
) ENGINE = InnoDB;
CREATE TABLE `group_alias` (
`group_id` INT UNSIGNED NOT NULL,
`alias` VARCHAR(256),
CONSTRAINT `alias_group_id`
FOREIGN KEY (`group_id`)
REFERENCES `group` (`group_id`),
FULLTEXT INDEX `search` (`alias`)
) ENGINE = InnoDB;
CREATE TABLE `item` (
`item_id` INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
`group_id` INT UNSIGNED,
`name` VARCHAR(255) NOT NULL,
CONSTRAINT `item_group_id`
FOREIGN KEY (`group_id`)
REFERENCES `group` (`group_id`),
FULLTEXT INDEX `search` (`name`)
) ENGINE = InnoDB;
CREATE TABLE `item_with_unique` LIKE `item`;
ALTER TABLE `item_with_unique` ADD UNIQUE INDEX `unique_item_group` (`group_id`, `name`);
INSERT INTO `group` (`group_id`, `name`) VALUES (1, 'Thompson');
INSERT INTO `group` (`group_id`, `name`) VALUES (2, 'MacDonald');
INSERT INTO `group` (`group_id`, `name`) VALUES (3, 'Stewart');
INSERT INTO `group_alias` (`group_id`, `alias`) VALUES (1, 'Tomson');
INSERT INTO `group_alias` (`group_id`, `alias`) VALUES (2, 'Something');
INSERT INTO `group_alias` (`group_id`, `alias`) VALUES (3, 'MacStewart');
INSERT INTO `item` (`item_id`, `group_id`, `name`) VALUES (1, 1, 'MacTavish');
INSERT INTO `item` (`item_id`, `group_id`, `name`) VALUES (2, 1, 'MacTavish; Red');
INSERT INTO `item` (`item_id`, `group_id`, `name`) VALUES (3, 2, 'MacAgnew');
INSERT INTO `item` (`item_id`, `group_id`, `name`) VALUES (4, 3, 'Spider');
INSERT INTO `item` (`item_id`, `group_id`, `name`) VALUES (5, 2, 'blahblah');
INSERT INTO `item_with_unique` SELECT * FROM `item`;
SELECT `i`.`item_id`, `g_a`.`alias` AS `group`, `i`.`name` AS `name`,
IF(MATCH (`g_a`.`alias`) AGAINST ('Mac*' IN BOOLEAN MODE), 1, 0) AS `group_match`,
IF(MATCH (`i`.`name`) AGAINST ('Mac*' IN BOOLEAN MODE), 1, 0) AS `item_match`
FROM `item` `i`
JOIN `group_alias` `g_a` USING (group_id)
WHERE
MATCH (`g_a`.`alias`) AGAINST ('Mac*' IN BOOLEAN MODE)
OR
MATCH (`i`.`name`) AGAINST ('Mac*' IN BOOLEAN MODE);
SELECT "Same query, using table with unique index (NOTE: sporadically this is actually correct, in such case, skip to bottom notes)";
SELECT `i`.`item_id`, `g_a`.`alias` AS `group`, `i`.`name` AS `name`,
IF(MATCH (`g_a`.`alias`) AGAINST ('Mac*' IN BOOLEAN MODE), 1, 0) AS `group_match`,
IF(MATCH (`i`.`name`) AGAINST ('Mac*' IN BOOLEAN MODE), 1, 0) AS `item_match`
FROM `item_with_unique` `i`
JOIN `group_alias` `g_a` USING (group_id)
WHERE
MATCH (`g_a`.`alias`) AGAINST ('Mac*' IN BOOLEAN MODE)
OR
MATCH (`i`.`name`) AGAINST ('Mac*' IN BOOLEAN MODE);
SELECT "Union of the two OR match conditions seperately (expected result from second query)";
SELECT `i`.`item_id`, `g_a`.`alias` AS `group`, `i`.`name` AS `name`,
IF(MATCH (`g_a`.`alias`) AGAINST ('Mac*' IN BOOLEAN MODE), 1, 0) AS `group_match`,
IF(MATCH (`i`.`name`) AGAINST ('Mac*' IN BOOLEAN MODE), 1, 0) AS `item_match`
FROM `item_with_unique` `i`
JOIN `group_alias` `g_a` USING (group_id)
WHERE
MATCH (`g_a`.`alias`) AGAINST ('Mac*' IN BOOLEAN MODE)
UNION
SELECT `i`.`item_id`, `g_a`.`alias` AS `group`, `i`.`name` AS `name`,
IF(MATCH (`g_a`.`alias`) AGAINST ('Mac*' IN BOOLEAN MODE), 1, 0) AS `group_match`,
IF(MATCH (`i`.`name`) AGAINST ('Mac*' IN BOOLEAN MODE), 1, 0) AS `item_match`
FROM `item_with_unique` `i`
JOIN `group_alias` `g_a` USING (group_id)
WHERE
MATCH (`i`.`name`) AGAINST ('Mac*' IN BOOLEAN MODE);
SELECT "Now rebuild the schema (add a newline somewhere so sqlfiddle thinks it has changed) and observe that the results of the second query. It may take multiple attempts but it usually cycles between 3 states:";
SELECT "1: Returns ALL results as if there were no conditions (5 rows)";
SELECT "2: Returns results as if there were no second part to the OR condition (1 row)";
SELECT "3: Returns the correct results (rarely)";
如果你有一个单词的名字和别名。您正在检查整数值或前导数值。那么全文不是您需要的索引类型 一个简单的
索引(名称)
,再加上像“Mac%”这样的名称将非常有效
如果你有很多单词的长短语,而“麦克唐纳德”可能在中间,那么<代码>全文> <代码> >代码>匹配…反对
是正确的做法
无论是哪种类型的索引
WHERE table1 ...
OR table2 ...
这将是低效的。粗略地说,优化器必须进行“交叉连接”,以获得两个表之间的所有行组合,然后查看其中哪一个匹配一个或其他匹配/相似项
也许您已经“过度规范化”了数据?
名称
和别名
不能在同一个表中吗?查询速度会快得多,而且会有优化技术使其更快。你所拥有的将会非常缓慢,只有1K行;我的建议可以优化数百万行,甚至数十亿行。尝试在您的语句中使用忽略索引
:
SELECT `i`.`item_id`, `g_a`.`alias` AS `group`, `i`.`name` AS `name`
FROM `item` `i`
IGNORE INDEX (unique_item_group)
JOIN `group_alias` `g_a` USING (group_id)
WHERE
MATCH (`g_a`.`alias`) AGAINST ('Mac*' IN BOOLEAN MODE)
OR
MATCH (`i`.`name`) AGAINST ('Mac*' IN BOOLEAN MODE);
MySQL在随机使用
unique\u item\u group
进行全文搜索时表现出难以置信的愚蠢。关于效率低下的问题。首先,这只是一个示例数据集-全文是我要寻找的。而且它没有过度规范化,因为项目可以有多个别名。关于您对交叉连接的评论,这肯定会受到正在搜索的两个表之间现有的内部连接的限制,因此不会表现得很差?我不明白为什么它必须交叉连接上面的所有行,但我可能弄错了。请提供EXPLAIN SELECT…
——我认为它将显示交叉连接(通过说出ALL和ALL)。问题在于跨两个表的或。我可以想象一个丑陋的混乱,包括一个联合
(避免或
,允许优化器在每个表上使用全文
),以及一些子查询来重新组合这些内容。我来解决这个问题好吗?你说得对,它确实说明了一切。然而,union备选方案看起来并没有太好,有2个全文和3个ALL。我想我可能需要考虑一个完全不同的方法-谢谢你把这件事引起我的注意。然而,我仍然对抽象奇怪的mysql行为感兴趣。我找到了一个更好的解决方案,使用缓存表,使所有全文索引都在同一个表上-再次感谢您的建议。请向我展示查询和解释;有些东西不起作用;它不应该说全部,这是正确的答案。谢谢