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12.7.1 Boolean Full-Text Searches
---------------------------------
MySQL can perform boolean full-text searches using the `IN BOOLEAN
MODE' modifier:
mysql> SELECT * FROM articles WHERE MATCH (title,body)
-> AGAINST ('+MySQL -YourSQL' IN BOOLEAN MODE);
+----+-----------------------+-------------------------------------+
| id | title | body |
+----+-----------------------+-------------------------------------+
| 1 | MySQL Tutorial | DBMS stands for DataBase ... |
| 2 | How To Use MySQL Well | After you went through a ... |
| 3 | Optimizing MySQL | In this tutorial we will show ... |
| 4 | 1001 MySQL Tricks | 1. Never run mysqld as root. 2. ... |
| 6 | MySQL Security | When configured properly, MySQL ... |
+----+-----------------------+-------------------------------------+
The `+' and `-' operators indicate that a word is required to be
present or absent, respectively, for a match to occur. Thus, this query
retrieves all the rows that contain the word `MySQL' but that do _not_
contain the word `YourSQL'.
Boolean full-text searches have these characteristics:
* They do not use the 50% threshold.
* They do not automatically sort rows in order of decreasing
relevance. You can see this from the preceding query result: The
row with the highest relevance is the one that contains `MySQL'
twice, but it is listed last, not first.
* They can work even without a `FULLTEXT' index, although a search
executed in this fashion would be quite slow.
* The minimum and maximum word length full-text parameters apply.
* The stopword list applies.
The boolean full-text search capability supports the following
operators:
* `+'
A leading plus sign indicates that this word _must_ be present in
each row 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.'
* (no operator)
By default (when neither `+' nor `-' is specified) the word is
optional, but the rows that contain it are rated higher. This
mimics the behavior of `MATCH() ... AGAINST()' without the `IN
BOOLEAN MODE' modifier.
* `> <'
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
the example following this list.
* `( )'
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 should be _appended_ to the word to
be affected. Words match if they begin with the word preceding the
`*' operator.
* `"'
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, performs a search in the `FULLTEXT' index for the words.
Prior to MySQL 5.0.3, the engine then performed a substring search
for the phrase in the records that were found, so the match must
include non-word characters in the phrase. As of MySQL 5.0.3,
non-word 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"' in MySQL 5.0.3, but not before.
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 following examples demonstrate some search strings that use boolean
full-text operators:
* `'apple banana''
Find rows that contain at least one of the two words.
* `'+apple +juice''
Find rows that contain both words.
* `'+apple macintosh''
Find rows that contain the word `apple', but rank rows higher if
they also contain `macintosh'.
* `'+apple -macintosh''
Find rows that contain the word `apple' but not `macintosh'.
* `'+apple ~macintosh''
Find rows that contain the word `apple', but if the row also
contains the word `macintosh', rate it lower than if row does not.
This is `softer' than a search for `'+apple -macintosh'', for
which the presence of `macintosh' causes the row not to be returned
at all.
* `'+apple +(>turnover <strudel)''
Find rows that contain the words `apple' and `turnover', or
`apple' and `strudel' (in any order), but rank `apple turnover'
higher than `apple strudel'.
* `'apple*''
Find rows that contain words such as `apple', `apples',
`applesauce', or `applet'.
* `'"some words"''
Find rows that contain the exact phrase `some words' (for example,
rows that contain `some words of wisdom' but not `some noise
words'). Note that the ‘`"'’ characters that enclose the
phrase are operator characters that delimit the phrase. They are
not the quotes that enclose the search string itself.
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