A full-text index in MySQL is an index of type FULLTEXT. Full-text indexes can be used only with InnoDB or MyISAM tables, and can be created only for CHAR , VARCHAR , or TEXT columns. MySQL provides a built-in full-text ngram parser that supports Chinese, Japanese, and Korean (CJK), and an installable MeCab full-text parser plugin for Japanese. A FULLTEXT index definition can be given in the CREATE TABLE statement when a table is created, or added later using ALTER TABLE or CREATE INDEX . For large data sets, it is much faster to load your data into a table that has no FULLTEXT index and then create the index after that, than to load data into a table that has an existing FULLTEXT index.
3 types of full-text searches
- A natural language search interprets the search string as a phrase in natural human language (a phrase in free text). Full-text searches are natural language searches if the
IN NATURAL LANGUAGE MODE modifier is given or if no modifier is given.
- A boolean search interprets the search string using the rules of a special query language. The string contains the words to search for. It can also contain operators that specify requirements such that a word must be present or absent in matching rows, or that it should be weighted higher or lower than usual. Certain common words (stopwords) are omitted from the search index and do not match if present in the search string. The
IN BOOLEAN MODE modifier specifies a boolean search.
- A query expansion search is a modification of a natural language search. The search string is used to perform a natural language search. Then words from the most relevant rows returned by the search are added to the search string and the search is done again. The query returns the rows from the second search. The
IN NATURAL LANGUAGE MODE WITH QUERY EXPANSION or WITH QUERY EXPANSION modifier specifies a query expansion search.
Create full-text indexes
// Add FULLTEXT KEY on table creation
CREATE TABLE user (
id INT NOT NULL AUTO_INCREMENT,
first_name varchar(255) DEFAULT NULL,
last_name varchar(255) DEFAULT NULL,
email varchar(255) DEFAULT NULL,
PRIMARY KEY (id),
FULLTEXT KEY (first_name,last_name,email)
);
ALTER TABLE user
ADD FULLTEXT(first_name,last_name,email);
Note that once you full-text index a table, you have to specify all full-text indexed columns of that table on your query.
SELECT * FROM user
WHERE MATCH (first_name,last_name,email)
AGAINST ('folau' WITH QUERY EXPANSION);