带有全文索引的 MySQL 索引提示

Question

我在使用全文索引时遇到问题并尝试同时使用索引提示。 这是一个示例表：

CREATE TABLE IF NOT EXISTS `products` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `idcategory` bigint(20) NOT NULL,
  `name` text NOT NULL,
  `short_description` text,
  `description` longtext NOT NULL,
  PRIMARY KEY (`id`),
  KEY `idcategory` (`idcategory`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

ALTER TABLE `products` ADD FULLTEXT INDEX `name_fulltext` (`name`);
ALTER TABLE `products` ADD FULLTEXT INDEX `short_description_fulltext` (`short_description`);
ALTER TABLE `products` ADD FULLTEXT INDEX `description_fulltext` (`description`);

此查询运行良好：

SELECT *
FROM products USE INDEX (idcategory)
WHERE idcategory = 1

此查询运行良好：

SELECT *
FROM products AS p
WHERE p.idcategory = 1
AND (
    MATCH(p.name) AGAINST ("*test*" IN BOOLEAN MODE)
    OR MATCH(p.short_description) AGAINST ("*test*" IN BOOLEAN MODE)
    OR MATCH(p.description) AGAINST ("*test*" IN BOOLEAN MODE)
)

此查询有错误：

SELECT *
FROM products AS p USE INDEX (idcategory)
WHERE p.idcategory = 1
AND (
    MATCH(p.name) AGAINST ("*test*" IN BOOLEAN MODE)
    OR MATCH(p.short_description) AGAINST ("*test*" IN BOOLEAN MODE)
    OR MATCH(p.description) AGAINST ("*test*" IN BOOLEAN MODE)
)

Error: #1191 - Can't find FULLTEXT index matching the column list

我不明白为什么没有使用索引以及为什么它要寻找 FULTEXT 索引来匹配。 匹配什么？

从文档（ https://dev.mysql.com/doc/refman/8.0/en/index-hints.html ）：

对于布尔模式搜索，带有 FOR ORDER BY 或 FOR GROUP BY 的索引提示将被静默忽略。 使用 FOR JOIN 或没有 FOR 修饰符的索引提示得到尊重。 与提示应用于非全文搜索的方式不同，提示用于查询执行的所有阶段（查找行和检索、分组和排序）。 即使为非 FULLTEXT 索引给出提示，也是如此。

那么问题是什么？ 它表示即使在 FULLTEXT 搜索的情况下为非 FULLTEXT 索引给出了提示，索引也会得到遵守。 我错过了什么吗？ 我误解了文档吗？

谢谢您阅读此篇。

Answer 1

** 11/10 编辑 **

崩溃并开始摆弄自己。 经过一些研究和测试，我将这组查询放在一起，希望能有助于阐明一些额外的问题。 （我使用了dbfiddle 。请注意，失败的查询已被注释掉，因为如果保留，则不会运行其他任何内容，至少在dbfiddle 上。）

尝试运行这些，希望输出和注释能最好地解释。 特别是，查询集 7 和 8 展示了如何设置多列 FULLTEXT INDEX，因为我认为这可能是您在这里的最终意图。

-------------------------------- Query Set 1 ------------------------------------
-- Only possible key is `idcategory`, because each FULLTEXT INDEX is for a single 
-- column, but using 3 different MATCH clauses, each for a different column. 
-- (i.e. Can't index into all 3 simultaneously using only a single column index.)
-- Keys/Indexes on `idcategory`.

DROP TABLE IF EXISTS `products`;

CREATE TABLE `products` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `idcategory` bigint(20) NOT NULL,
  `name` text NOT NULL,
  `short_description` text,
  `description` longtext NOT NULL,
  PRIMARY KEY (`id`),
  KEY `idcategory` (`idcategory`),
  FULLTEXT INDEX `name_fulltext` (`name`),
  FULLTEXT INDEX `short_description_fulltext` (`short_description`),
  FULLTEXT INDEX `description_fulltext` (`description`)  
) ENGINE=InnoDB DEFAULT CHARSET=utf8;


INSERT INTO `products` (`idcategory`, `name`, `short_description`, `description`)
VALUES (1, 'test1', 'sdesc1', 'desc1'), (1, 'test2', 'sdesc2', 'desc2'), (2, 'test3', 'sdesc3', 'desc3');

EXPLAIN SELECT *
FROM products AS p
WHERE p.idcategory = 1
AND (
    MATCH(p.name) AGAINST ("*test*" IN BOOLEAN MODE)
    OR MATCH(p.short_description) AGAINST ("*test*" IN BOOLEAN MODE)
    OR MATCH(p.description) AGAINST ("*test*" IN BOOLEAN MODE)
);

SELECT *
FROM products AS p
WHERE p.idcategory = 1
AND (
    MATCH(p.name) AGAINST ("*test*" IN BOOLEAN MODE)
    OR MATCH(p.short_description) AGAINST ("*test*" IN BOOLEAN MODE)
    OR MATCH(p.description) AGAINST ("*test*" IN BOOLEAN MODE)
);

-------------------------------- Query Set 2 ------------------------------------

-- Possible keys are `idcategory` and `name_fulltext`. All FULLTEXT INDEXES are 
-- single column, and only 1 MATCH clause [for a single column, `name`] is 
-- specified. Keys/Indexes on `name_fulltext`. (When faced with a choice of 
-- multiple indexes, the optimizer will choose the most selective option [i.e. 
-- that option with the lowest number of rows]).

DROP TABLE IF EXISTS `products`;

CREATE TABLE `products` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `idcategory` bigint(20) NOT NULL,
  `name` text NOT NULL,
  `short_description` text,
  `description` longtext NOT NULL,
  PRIMARY KEY (`id`),
  KEY `idcategory` (`idcategory`),
  FULLTEXT INDEX `name_fulltext` (`name`),
  FULLTEXT INDEX `short_description_fulltext` (`short_description`),
  FULLTEXT INDEX `description_fulltext` (`description`)  
) ENGINE=InnoDB DEFAULT CHARSET=utf8;


INSERT INTO `products` (`idcategory`, `name`, `short_description`, `description`)
VALUES (1, 'test1', 'sdesc1', 'desc1'), (1, 'test2', 'sdesc2', 'desc2'), (2, 'test3', 'sdesc3', 'desc3');

EXPLAIN SELECT *
FROM products AS p
WHERE p.idcategory = 1
AND (
    MATCH(p.name) AGAINST ("*test*" IN BOOLEAN MODE)
);

SELECT *
FROM products AS p
WHERE p.idcategory = 1
AND (
    MATCH(p.name) AGAINST ("*test*" IN BOOLEAN MODE)
);

-------------------------------- Query Set 3 ------------------------------------

-- Same as Query Set 2, but explicitly call for INDEX `name_fulltext`. Now only
-- possible key is name_fulltext.

DROP TABLE IF EXISTS `products`;

CREATE TABLE `products` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `idcategory` bigint(20) NOT NULL,
  `name` text NOT NULL,
  `short_description` text,
  `description` longtext NOT NULL,
  PRIMARY KEY (`id`),
  KEY `idcategory` (`idcategory`),
  FULLTEXT INDEX `name_fulltext` (`name`),
  FULLTEXT INDEX `short_description_fulltext` (`short_description`),
  FULLTEXT INDEX `description_fulltext` (`description`)  
) ENGINE=InnoDB DEFAULT CHARSET=utf8;


INSERT INTO `products` (`idcategory`, `name`, `short_description`, `description`)
VALUES (1, 'test1', 'sdesc1', 'desc1'), (1, 'test2', 'sdesc2', 'desc2'), (2, 'test3', 'sdesc3', 'desc3');

EXPLAIN SELECT *
FROM products AS p USE INDEX (`name_fulltext`)
WHERE p.idcategory = 1 
AND (
    MATCH(p.name) AGAINST ("*test*" IN BOOLEAN MODE)
);

SELECT *
FROM products AS p USE INDEX (`name_fulltext`)
WHERE p.idcategory = 1
AND (
    MATCH(p.name) AGAINST ("*test*" IN BOOLEAN MODE)
);

-------------------------------- Query Set 4 ------------------------------------
----------------------------------- FAILS ---------------------------------------
-- Same as Query Set 1 but trying to force INDEX `name_fulltext`. Doesn't work
-- because `name_fulltext` only indexes a single column, but MATCH / AGAINST
-- has three different clauses, each specifying a different column. (And hence
-- why the only possible key is `idcategory`, as shown in output of EXPLAIN, 
-- Query Set 1.)

--DROP TABLE IF EXISTS `products`;

--CREATE TABLE `products` (
--  `id` bigint(20) NOT NULL AUTO_INCREMENT,
--  `idcategory` bigint(20) NOT NULL,
--  `name` text NOT NULL,
--  `short_description` text,
--  `description` longtext NOT NULL,
--  PRIMARY KEY (`id`),
--  KEY `idcategory` (`idcategory`),
--  FULLTEXT INDEX `name_fulltext` (`name`),
--  FULLTEXT INDEX `short_description_fulltext` (`short_description`),
--  FULLTEXT INDEX `description_fulltext` (`description`)  
--) ENGINE=InnoDB DEFAULT CHARSET=utf8;


--INSERT INTO `products` (`idcategory`, `name`, `short_description`, `description`)
--VALUES (1, 'test1', 'sdesc1', 'desc1'), (1, 'test2', 'sdesc2', 'desc2'), (2, 'test3', 'sdesc3', 'desc3');

--EXPLAIN SELECT *
--FROM products AS p USE INDEX (`name_fulltext`)
--WHERE p.idcategory = 1
--AND (
--    MATCH(p.name) AGAINST ("*test*" IN BOOLEAN MODE)
--    OR MATCH(p.short_description) AGAINST ("*test*" IN BOOLEAN MODE)
--    OR MATCH(p.description) AGAINST ("*test*" IN BOOLEAN MODE)
--);

--SELECT *
--FROM products AS p USE INDEX (`name_fulltext`)
--WHERE p.idcategory = 1
--AND (
--    MATCH(p.name) AGAINST ("*test*" IN BOOLEAN MODE)
--    OR MATCH(p.short_description) AGAINST ("*test*" IN BOOLEAN MODE)
--    OR MATCH(p.description) AGAINST ("*test*" IN BOOLEAN MODE)
--);


-------------------------------- Query Set 5 ------------------------------------
----------------------------------- FAILS ---------------------------------------

-- Trying to force keying/indexing on `idcategory` instead of `name_fulltext`. 
-- Doesn't work because `idcategory` is not established as a FULLTEXT INDEX, 
-- which is required for MATCH / AGAINST? It keyed on this field when not 
-- explicitly calling USE INDEX and no other index was possible, and when
-- explicitly calling USE INDEX but with no MATCH / AGAINST call, so
-- this behavior seems a bit inconsistent.

--DROP TABLE IF EXISTS `products`;

--CREATE TABLE `products` (
--  `id` bigint(20) NOT NULL AUTO_INCREMENT,
--  `idcategory` bigint(20) NOT NULL,
--  `name` text NOT NULL,
--  `short_description` text,
--  `description` longtext NOT NULL,
--  PRIMARY KEY (`id`),
--  KEY `idcategory` (`idcategory`),
--  FULLTEXT INDEX `name_fulltext` (`name`),
--  FULLTEXT INDEX `short_description_fulltext` (`short_description`),
--  FULLTEXT INDEX `description_fulltext` (`description`)  
--) ENGINE=InnoDB DEFAULT CHARSET=utf8;


--INSERT INTO `products` (`idcategory`, `name`, `short_description`, `description`)
--VALUES (1, 'test1', 'sdesc1', 'desc1'), (1, 'test2', 'sdesc2', 'desc2'), (2, 'test3', 'sdesc3', 'desc3');

--EXPLAIN SELECT *
--FROM products AS p USE INDEX (`idcategory`)
--WHERE p.idcategory = 1 
--AND (
--    MATCH(p.name) AGAINST ("*test*" IN BOOLEAN MODE)
--);

--SELECT *
--FROM products AS p USE INDEX (`idcategory`)
--WHERE p.idcategory = 1
--AND (
--   MATCH(p.name) AGAINST ("*test*" IN BOOLEAN MODE)
--);

-------------------------------- Query Set 6 ------------------------------------
----------------------------------- FAILS ---------------------------------------

-- We can't make `idcategory` a FULLTEXT INDEX of course, because it is a 
-- bigint(20). (Could try making this KEY a text field instead, 
-- see if error persists...)

--DROP TABLE IF EXISTS `products`;

--CREATE TABLE `products` (
--  `id` bigint(20) NOT NULL AUTO_INCREMENT,
--  `idcategory` bigint(20) NOT NULL,
--  `name` text NOT NULL,
--  `short_description` text,
--  `description` longtext NOT NULL,
--  PRIMARY KEY (`id`),
--  KEY `idcategory` (`idcategory`),
--  FULLTEXT INDEX `idcategory_fulltext` (`idcategory`) 
--) ENGINE=InnoDB DEFAULT CHARSET=utf8;


--INSERT INTO `products` (`idcategory`, `name`, `short_description`, `description`)
--VALUES (1, 'test1', 'sdesc1', 'desc1'), (1, 'test2', 'sdesc2', 'desc2'), (2, 'test3', 'sdesc3', 'desc3');

--EXPLAIN SELECT *
--FROM products AS p USE INDEX (`idcategory`)
--WHERE p.idcategory = 1 
--AND (
--    MATCH(p.name) AGAINST ("*test*" IN BOOLEAN MODE)
--);

--SELECT *
--FROM products AS p USE INDEX (`idcategory`)
--WHERE p.idcategory = 1
--AND (
--    MATCH(p.name) AGAINST ("*test*" IN BOOLEAN MODE)
--);

-------------------------------- Query Set 7 ------------------------------------

-- A multi-column index. The MATCH / AGAINST search functions like an 'OR' 
-- clause for all three columns. (i.e. if the text pattern is present in any
-- of the three columns, a match is found). Must specify all three columns in MATCH
-- clause, because the FULLTEXT INDEX includes all three.
-- Keys/Indexes on 'name_sdesc_desc_fulltext` (multi-column fulltext index),
-- but shows `idcategory` as possible index.
-- (Perhaps when all is said and done this is the desired behavior?)

DROP TABLE IF EXISTS `products`;

CREATE TABLE `products` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `idcategory` bigint(20) NOT NULL,
  `name` text NOT NULL,
  `short_description` text,
  `description` longtext NOT NULL,
  PRIMARY KEY (`id`),
  KEY `idcategory` (`idcategory`),
  FULLTEXT INDEX `name_sdesc_desc_fulltext` (`name`, `short_description`, `description`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;


INSERT INTO `products` (`idcategory`, `name`, `short_description`, `description`)
VALUES (1, 'test1', 'sdesc1', 'desc1'), (1, 'test2', 'sdesc2', 'desc2'), (2, 'test3', 'sdesc3', 'desc3');

EXPLAIN SELECT *
FROM products AS p
WHERE p.idcategory = 1
AND (
    MATCH(p.name, p.short_description, p.description) AGAINST ("*test*" IN BOOLEAN MODE)
);

SELECT *
FROM products AS p
WHERE p.idcategory = 1
AND (
    MATCH(p.name, p.short_description, p.description) AGAINST ("*test*" IN BOOLEAN MODE)
);

-------------------------------- Query Set 8 ------------------------------------

-- Same as Query Set 7, but explicitly calls for `name_sdesc_desc` FULLTEXT INDEX.
-- Now, only possible index is `name_sdesc_desc_fulltext`.

DROP TABLE IF EXISTS `products`;

CREATE TABLE `products` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `idcategory` bigint(20) NOT NULL,
  `name` text NOT NULL,
  `short_description` text,
  `description` longtext NOT NULL,
  PRIMARY KEY (`id`),
  KEY `idcategory` (`idcategory`),
  FULLTEXT INDEX `name_sdesc_desc_fulltext` (`name`, `short_description`, `description`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;


INSERT INTO `products` (`idcategory`, `name`, `short_description`, `description`)
VALUES (1, 'test1', 'sdesc1', 'desc1'), (1, 'test2', 'sdesc2', 'desc2'), (2, 'test3', 'sdesc3', 'desc3');

EXPLAIN SELECT *
FROM products AS p USE INDEX (`name_sdesc_desc`)
WHERE p.idcategory = 1
AND (
    MATCH(p.name, p.short_description, p.description) AGAINST ("*test*" IN BOOLEAN MODE)
);

SELECT *
FROM products AS p USE INDEX (`name_sdesc_desc`)
WHERE p.idcategory = 1
AND (
    MATCH(p.name, p.short_description, p.description) AGAINST ("*test*" IN BOOLEAN MODE)
);