User Guide

This function performs a search where the query represents a phrase in natural human language with no special operators. The results are ranked in order by relevance.

A phrase that is enclosed within double quote (") characters matches only rows that contain the phrase literally, as it was typed. The full-text engine splits the phrase into words and performs a search in the FULLTEXT index for the words. Nonword characters need not be matched exactly: Phrase searching requires only that matches contain exactly the same words as the phrase and in the same order. For example, "test phrase" matches "test, phrase". If the phrase contains no words that are in the index, the result is empty. For example, if all words are either stopwords or shorter than the minimum length of indexed words, the result is empty.

The MySQL FULLTEXT implementation regards any sequence of true word characters (letters, digits, and underscores) as a word. That sequence may also contain apostrophes ('), but not more than one in a row. This means that aaa'bbb is regarded as one word, but aaa''bbb is regarded as two words. Apostrophes at the beginning or the end of a word are stripped by the FULLTEXT parser; 'aaa'bbb' would be parsed as aaa'bbb.

Some words are ignored in full-text searches:

• Any word that is too short is ignored. The default minimum length of words that are found by full-text searches is three characters.
• Words in the stopword list are ignored. A stopword is a word such as “the” or “some” that is so common that it is considered to have zero semantic value.

Every correct word in the collection and in the query is weighted according to its significance in the collection or query. Thus, a word that is present in many documents has a lower weight, because it has lower semantic value in this particular collection. Conversely, if the word is rare, it receives a higher weight. The weights of the words are combined to compute the relevance of the row. This technique works best with large collections.

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For more information, please visit the MySQL Reference Manual.

Full-text search supports query expansion. This is generally useful when a search phrase is too short, which often means that the user is relying on implied knowledge that the full-text search engine lacks. It works by performing the search twice, where the search phrase for the second search is the original search phrase concatenated with the few most highly relevant documents from the first search. Note: Because blind query expansion tends to increase noise significantly by returning nonrelevant documents, use it only when a search phrase is short.

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For more information, please visit the MySQL Reference Manual.

A boolean search interprets the search query using the rules of a special query language. The query contains the words to search for, including operators that specify requirements such that a word must be present or absent in matching results, or that it should be weighted higher or lower than usual.

The boolean full-text search capability supports the following operators:

A leading plus sign indicates that this word must be present in each result that is returned.

A leading minus sign indicates that this word must not be present in any of the rows that are returned.

Note: The - operator acts only to exclude rows that are otherwise matched by other search terms. Thus, a boolean-mode search that contains only terms preceded by - returns an empty result. It does not return "all rows except those containing any of the excluded terms."

By default (when neither + nor - is specified), the word is optional, but the rows that contain it are rated higher.

This operator tests whether two or more words all start within a specified distance from each other, measured in words. Specify the search words within a double-quoted string immediately before the @distance operator, for example, "word1 word2 word3" @8.

These two operators are used to change a word's contribution to the relevance value that is assigned to a row. The > operator increases the contribution and the < operator decreases it. See an example.

Parentheses group words into subexpressions. Parenthesized groups can be nested.

A leading tilde acts as a negation operator, causing the word's contribution to the row's relevance to be negative. This is useful for marking “noise” words. A row containing such a word is rated lower than others, but is not excluded altogether, as it would be with the - operator.

The asterisk serves as the truncation (or wildcard) operator. Unlike the other operators, it is appended to the word to be affected. Words match if they begin with the word preceding the * operator.

If a word is specified with the truncation operator, it is not stripped from a boolean query, even if it is too short or a stopword.

The wildcarded word is considered as a prefix that must be present at the start of one or more words. If the minimum word length is 4, a search for +word +the* could return fewer rows than a search for +word +the, because the second query ignores the too-short search term the.

A phrase that is enclosed within double quote (") characters matches only rows that contain the phrase literally, as it was typed. The full-text engine splits the phrase into words and performs a search in the FULLTEXT index for the words. Nonword characters need not be matched exactly: Phrase searching requires only that matches contain exactly the same words as the phrase and in the same order. For example, "test phrase" matches "test, phrase".

If the phrase contains no words that are in the index, the result is empty. The words might not be in the index because of a combination of factors: if they do not exist in the text, are stopwords, or are shorter than the minimum length of indexed words.

• +
• -
• (no operator)
• @distance
• > <
• ( )
• ~
• *
• "

For example queries, please see Appendix A: Example queries using boolean search mode

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For more information, please visit the MySQL Reference Manual.