前言
最近在学习和了解 MySQL 8 自带的全文搜索功能。自己在看资料的时候顺便翻译了一下，希望对大家有用。（章节序号可能有所差异，因为官方文档会不定期更新）
官方原文链接如下：《Full-Text Stopwords》
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）加载和搜索停用字列表以进行全文查询。如果用于全文索引或搜索的停用字文件或列的字符集或排序规则与character_set_server或collation_server不同，则停用字查找可能会出现错误的命中或未命中。
停用字查找的大小写区分取决于服务器排序规则。例如，如果排序规则 utf8mb4_0900_ai_ci，则查找不区分大小写，而如果排序规则为 utf8mb4_0900_as_cs 或 utf8mb4_bin，则查找区分大小写。
InnoDB 搜索索引的停用字
MyISAM 搜索索引的停用字
InnoDB 搜索索引的停用字
InnoDB 的默认停用字列表相对较短，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，您可以搜索“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单词。
要查看默认的 InnoDB 停用字列表，请查询 Information_schema 数据库模式下的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)
要为所有 InnoDB 表定义自己的停用字列表，请定义一个与INNODB_FT_DEFAULT_STOPWORD表结构相同的表，用停用字填充该表，并在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 形式的值。停用字表必须具有一个名为 value 的 VARCHAR 列。以下示例演示了如何为 InnoDB 创建和配置新的全局停用字表。
-- Create a new stopword table mysql> 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 table mysql> 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 table
mysql> 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 table mysql> 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 数据库模式下 INNODB_FT_INDEX_TABLE 表来验证指定的停用字（“Ishmael”）是否未显示。
注意
默认情况下，长度小于 3 个字符或长度大于 84 个字符的单词不会出现在 InnoDB 全文搜索索引中。最大和最小字长值可使用 innodb_ft_max_token_size 和 innodb_ft_min_token_size 变量进行配置。此默认行为不适用于 ngram 解析器插件。NGRAM 字长大小由 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)
若要逐表创建停用字表，请创建其他停用字表，并使用 innodb_ft_user_stopword_table 选项指定要使用的停用字表。
MyISAM 搜索索引的停用词
如果停用字文件是 ucs2、utf16、utf16le 或 utf32，则使用 latin1 加载和搜索 character_set_server。
若要覆盖 MyISAM 表的默认停用字列表，请设置 ft_stopword_file 系统变量。(参阅 Server System Variables.) 变量值应为包含停用字列表的文件的路径名，或用于禁用停用字筛选的空字符串。 服务器在数据目录中查找文件，除非给出绝对路径名来指定其他目录。更改此变量的值或停用字文件的内容后，重新启动服务器并重新生成 FULLTEXT 索引。
停用字列表是自由格式的，用于分隔具有任何非字母数字字符（如换行符、空格或逗号）的停用字。下划线字符 （_） 和单个撇号 （'） 除外，它们被视为单词的一部分。停用字列表的字符集是服务器的默认字符集;参阅 Server Character Set and Collation.
以下列表显示了 MyISAM 搜索索引的默认停用字。 在MySQL源代码发行版中，您可以在storage/myisam/ft_static.c文件中找到此列表。
a's able about above according accordingly across actually after afterwards again against ain't all allow allows almost alone along already also although always am among amongst an and another any anybody anyhow anyone anything anyway anyways anywhere apart appear appreciate appropriate are aren't around as aside ask asking associated at available away awfully be became because become becomes becoming been before beforehand behind being believe below beside besides best better between beyond both brief but by c'mon c's came can can't cannot cant cause causes certain certainly changes clearly co com come comes concerning consequently consider considering contain containing contains corresponding could couldn't course currently definitely described despite did didn't different do does doesn't doing don't done down downwards during each edu eg eight either else elsewhere enough entirely especially et etc even ever every everybody everyone everything everywhere ex exactly example except far few fifth first five followed following follows for former formerly forth four from further furthermore get gets getting given gives go goes going gone got gotten greetings had hadn't happens hardly has hasn't have haven't having he he's hello help hence her here here's hereafter hereby herein hereupon hers herself hi him himself his hither hopefully how howbeit however i'd i'll i'm i've ie if ignored immediate in inasmuch inc indeed indicate indicated indicates inner insofar instead into inward is isn't it it'd it'll it's its itself just keep keeps kept know known knows last lately later latter latterly least less lest let let's like liked likely little look looking looks ltd mainly many may maybe me mean meanwhile merely might more moreover most mostly much must my myself name namely nd near nearly necessary need needs neither never nevertheless new next nine no nobody non none noone nor normally not nothing novel now nowhere obviously of off often oh ok okay old on once one ones only onto or other others otherwise ought our ours ourselves out outside over overall own particular particularly per perhaps placed please plus possible presumably probably provides que quite qv rather rd re really reasonably regarding regardless regards relatively respectively right said same saw say saying says second secondly see seeing seem seemed seeming seems seen self selves sensible sent serious seriously seven several shall she should shouldn't since six so some somebody somehow someone something sometime sometimes somewhat somewhere soon sorry specified specify specifying still sub such sup sure t's take taken tell tends th than thank thanks thanx that that's thats the their theirs them themselves then thence there there's thereafter thereby therefore therein theres thereupon these they they'd they'll they're they've think third this thorough thoroughly those though three through throughout thru thus to together too took toward towards tried tries truly try trying twice two un under unfortunately unless unlikely until unto up upon us use used useful uses using usually value various very via viz vs want wants was wasn't way we we'd we'll we're we've welcome well went were weren't what what's whatever when whence whenever where where's whereafter whereas whereby wherein whereupon wherever whether which while whither who who's whoever whole whom whose why will willing wish with within without won't wonder would wouldn't yes yet you you'd you'll you're you've your yours yourself yourselves zero