全文终止词
使用服务器字符集和排序规则(character_set_server 和 collation_server 系统变量的值)加载终止词列表，进行全文搜索查询。如果用于全文索引或搜索的终止词文件或列的字符集或排序规则与 character_set_server 或 collation_server 不同，那么终止词查找可能会出现错误的命中或未命中。
终止词查找是否区分大小写取决于服务器的排序规则。例如，如果排序规则是 utf8mb4_0900_ai_ci，则查找不区分大小写，而如果排序规则是 utf8mb4_0900_as_cs 或 utf8mb4_bin，则查找区分大小写。
InnoDB 搜索索引的终止词
InnoDB 有一个相对较短的默认终止词列表，因为来自技术、文学和其他来源的文档通常使用短词作为关键字或重要短语。例如，您可能会搜索 “to be or not to be” 并期望得到一个合理的结果，而不是忽略所有这些词。
要查看默认 InnoDB 终止词列表，请查询 INFORMATION_SCHEMA.INNODB_FT_DEFAULT_STOPWORD 表。
mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_FT_DEFAULT_STOPWORD;+-------+| value |+-------+| a || about || an || are || as || at || be || by || com || de || en || for || from || how || i || in || is || it || la || of || on || or || that || the || this || to || was || what || when || where || who || will || with || und || the || www |+-------+36 rows in set (0.00 sec)
要对所有 InnoDB 表定义自己的终止词列表，需要定义一个表与 INNODB_FT_DEFAULT_STOPWORD 表相同的结构，并填充终止词，创建全文索引之前，将 innodb_ft_server_stopword_table 选项的值设置为 db_name/table_name 形式。终止词表必须有一个名为 value 的 VARCHAR 列。下面的示例演示如何为 InnoDB 创建和配置一个新的全局终止词表。
-- Create a new stopword tablemysql> CREATE TABLE my_stopwords(value VARCHAR(30)) ENGINE = INNODB;Query OK, 0 rows affected (0.01 sec)-- Insert stopwords (for simplicity, a single stopword is used in this example)mysql> INSERT INTO my_stopwords(value) VALUES ('Ishmael');Query OK, 1 row affected (0.00 sec)-- Create the tablemysql> CREATE TABLE opening_lines (id INT UNSIGNED AUTO_INCREMENT NOT NULL PRIMARY KEY,opening_line TEXT(500),author VARCHAR(200),title VARCHAR(200)) ENGINE=InnoDB;Query OK, 0 rows affected (0.01 sec)-- Insert data into the tablemysql> INSERT INTO opening_lines(opening_line,author,title) VALUES('Call me Ishmael.','Herman Melville','Moby-Dick'),('A screaming comes across the sky.','Thomas Pynchon','Gravity\'s Rainbow'),('I am an invisible man.','Ralph Ellison','Invisible Man'),('Where now? Who now? When now?','Samuel Beckett','The Unnamable'),('It was love at first sight.','Joseph Heller','Catch-22'),('All this happened, more or less.','Kurt Vonnegut','Slaughterhouse-Five'),('Mrs. Dalloway said she would buy the flowers herself.','Virginia Woolf','Mrs. Dalloway'),('It was a pleasure to burn.','Ray Bradbury','Fahrenheit 451');Query OK, 8 rows affected (0.00 sec)Records: 8 Duplicates: 0 Warnings: 0-- Set the innodb_ft_server_stopword_table option to the new stopword tablemysql> SET GLOBAL innodb_ft_server_stopword_table = 'test/my_stopwords';Query OK, 0 rows affected (0.00 sec)-- Create the full-text index (which rebuilds the table if no FTS_DOC_ID column is defined)mysql> CREATE FULLTEXT INDEX idx ON opening_lines(opening_line);Query OK, 0 rows affected, 1 warning (1.17 sec)Records: 0 Duplicates: 0 Warnings: 1
通过查询 INFORMATION_SCHEMA.INNODB_FT_INDEX_TABLE 中的词，可以验证指定的终止词 ('Ishmael') 是否存在。
注意
默认情况下，长度小于3个字符或大于84个字符的单词不会出现在 InnoDB 全文索引中。最大和最小字长值可以通过 innodb_ft_max_token_size 和 innodb_ft_min_token_size 变量进行配置。这个默认行为不适用于 ngram 解析器插件。ngram 标记的大小由 ngram_token_size 选项定义。
mysql> SET GLOBAL innodb_ft_aux_table='test/opening_lines';Query OK, 0 rows affected (0.00 sec)mysql> SELECT word FROM INFORMATION_SCHEMA.INNODB_FT_INDEX_TABLE LIMIT 15;+-----------+| word |+-----------+| across || all || burn || buy || call || comes || dalloway || first || flowers || happened || herself || invisible || less || love || man |+-----------+15 rows in set (0.00 sec)
要逐表创建终止词列表，请创建其他终止词表，并使用 innodb_ft_user_stopword_table 选项指定在创建全文索引之前要使用的终止词表。
MyISAM 搜索索引的终止词
如果 character_set_server 为 ucs2、utf16、utf16le 或 utf32，则使用 latin1加载终止词文件进行搜索。
要覆盖 MyISAM 表的默认终止词列表，请设置 ft_stopword_file 系统变量。变量值应该是包含终止词列表文件的路径名，或者是用于禁用终止词过滤的空字符串。服务器在数据目录中查找文件，除非指定了一个绝对路径名来指定另一个目录。在更改此变量的值或终止词文件的内容后，需要重新启动服务器并重建 FULLTEXT 索引。
终止词列表形式自由，用换行符、空格或逗号等任何非字母数字字符分隔终止词。例外是下划线字符(_)和单个撇号(')，它们被视为单词的一部分。终止词列表的字符集是服务器的默认字符集。
下面的列表显示了 MyISAM 搜索索引的默认终止词。在 MySQL 源代码分发版中，可以在 storage/myisam/ft_static.c 文件中找到此列表。
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官方网址：
https://dev.mysql.com/doc/refman/8.0/en/fulltext-stopwords.html
