The database search engine is MySQL. The search engine will retrieve all articles that have all of the keywords in them. The search is carried out against the author, title, and abstract fields in each record in the database. Partial word keywords will result in no records found. Search results with a word count of 1 have no associated abstract. Searching is case-insensitive.
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SEARCH EXAMPLES |
| back pain |
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Find abstracts that contain at least one of the words |
| pain* |
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Find abstracts that contain words such as "pain", "painful", "paint" etc. |
| +back +pain |
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Find abstracts that contain both words |
| +back -pain |
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Find abstracts that contain the word "back" but do not contain the word "pain" |
| ~back +pain |
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Find abstracts that contain the word "pain", but if the row also contains the word "back", rate it lower than if row does not |
| +back pain |
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Find abstracts that contain the word “back”, but rank rows higher if they also contain “pain”. |
| +back ~pain |
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Find abstrats that contain the word “back”, but if the row also contains the word “pain”, rate it lower than if row does not. This is “softer” than a search for '+back -pain', for which the presence of “pain” causes the row not to be returned at all. |
| +back +(>pain <injury) |
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Find abstracts that contain the words “back” and “pain”, or “back” and “injury” (in any order), but rank “back pain ” higher than “back injury ”. |
| "back pain" |
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Find abstracts that contain the exact phrase “back pain ” (for example, rows that contain “qigong for back pain ” but not “back problems including pain”). 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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SPECIAL NOTE: A search for the phrase "let it be" won't find any record, not even records containing something like "The Beatles: Let It Be". According to the MySQL team, this is not a bug. MySQL will sometimes take short words into consideration for phrase searches, but only if there is at least one properly long word in the search phrase. |
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SEARCH RULES |
| + |
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A leading plus sign indicates that this word must be present in each row that is returned. |
| - |
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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) |
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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. |
| > < |
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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. |
| () |
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Parentheses group words into subexpressions. Parenthesized groups can be nested. |
| ~ |
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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. |
| * |
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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.
If a word is specified with the truncation operator, it is not stripped from a boolean query, even if it is too short (as determined from the ft_min_word_len setting, which is 3) or a stopword. This occurs because the word is not seen as too short or a stopword, but as a prefix that must be present in the document in the form of a word that begins with the prefix. Suppose that ft_min_word_len=3. Then a search for '+word +the*' will likely return fewer rows than a search for '+word +the':
The former query remains as is and requires both word and the* (a word starting with the) to be present in the document.
The latter query is transformed to +word (requiring only word to be present). the is both too short and a stopword, and either condition is enough to cause it to be ignored. |
| " |
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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 statement used to search the database is MATCH()...AGAINST() in BOOLEAN MODE. MATCH() takes a comma-separated list that names the columns to be searched. These columns are fixed and cannot be modified by you: author, title, and abstract content. AGAINST takes a string to search for, and an optional modifier that indicates what type of search to perform. The search string must be a literal string.
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. Common words such as “some” or “then” are stopwords and do not match if present in the search string. The IN BOOLEAN MODE modifier specifies a boolean search. For complete information, see Section 11.8.2, “Boolean Full-Text Searches”.
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