i use this query for a fulltextsearch in my table:
SELECT Titel FROM cmsa WHERE MATCH(Titel) AGAINST ('+"Ort" +"Berlin"' IN BOOLEAN MODE)
but the result is empty.
If i use
SELECT Titel FROM cmsa WHERE Titel LIKE '%Berlin%'
the result would be (without quotes):
"Ort - Berlin"
Why the fulltextsearch didnt find this result. The word "Ort" and the word "Berlin" are both in the field Titel of the entry.
Other fulltext searches works great.
Any Idea?
I guess it is because MySQL has a server parameter - The minimum length of the word to be included in a FULLTEXT index. Default value for this parameter is 4 so your first word Ort is not included in this index. You should change this system parameter, restart server and then rebuild all FULLTEXT indexes.
REPAIR TABLE cmsa QUICK;
Change the full text index minimum word length with MySQL
Try without double quotes and make sure Mysql engine is MYISAM
SELECT
Titel
FROM
cmsa
WHERE
MATCH(Titel) AGAINST ('+Ort +Berlin' IN BOOLEAN MODE)
Some explanation
Boolean Mode Searches
SELECT headline, story FROM news
WHERE MATCH (headline,story)
AGAINST ('+Hurricane -Katrina' IN BOOLEAN MODE);
The above statement would match news stories about hurricanes but not those that mention hurricane katrina.
Query Expansion
The Blind Query Expansion (or automatic relevance feedback) feature can be used to expand the results of the search. This often includes much more noise, and makes for a very fuzzy search.
In most cases you would use this operation if the users query returned just a few results, you try it again WITH QUERY EXPANSION and it will add words that are commonly found with the words in the query.
SELECT headline, story FROM news
WHERE MATCH (headline,story)
AGAINST ('Katrina' WITH QUERY EXPANSION);
The above query might return all news stories about hurricanes, not just ones containing Katrina.
A couple points about Full-Text searching in MySQL:
Searches are not case sensitive
Short words are ignored, the default minimum length is 4 characters. You can change the min and max word length with the variables ft_min_word_len and ft_max_word_len
Words called stopwords are ignored, you can specify your own stopwords, but default words include the, have, some - see default
stopwords list.
You can disable stopwords by setting the variable ft_stopword_file to an empty string.
Full Text searching is only supported by the MyISAM storage engine.
If a word is present in more than 50% of the rows it will have a weight of zero. This has advantages on large datasets, but can make
testing difficult on small ones.
Your query was working perfectly for me. Please check your table is MYISAM or not because full text search working in only myisam engine.
Related
I have a mysql table and need to perform a fulltext search on it. However, even though the required data is in the table, fulltext search does not retrieve it.
Here is the query:
SELECT * from declensions_english where match(finite) against("did" IN BOOLEAN MODE)
The searched after data looks like this:
I did
Of course this is in the column called finite. There are about a million rows in the table beside this one, so wildcards are very slow.
Why is this not working? It's not because of the length of the word (did), because I've already set ft_min_word_len to 1. There are other cases with three letter words that deliver the expected outcome (i. e. the data is retrieved). But there are also cases where even four letter words are not found. I have no idea what's going on, but I am only using fulltext search since yesterday, so consider me a newbie here.
Since you use ft_min_word_len, I must assume that your table uses myisam table engine.
The word did is on the myisam stop word list, this is why the search does not return it.
You can either disable or change the stop word list or migrate to innodb, which does not have this word on its default stop word list.
To be honest, I cannot think of any reason to use myisam in 2019. You really should migrate over to innodb.
I have strings like the following in my VARCHAR InnoDB table column:
"This is a {{aaaa->bbb->cccc}} and that is a {{dddd}}!"
Now, I'd like to search for e.g. {{xxx->yyy->zzz}}. Brackets are part of the string. Sometimes searched together with another colum, but which only contains an ordinary id and hence don't need to be considered (I guess).
I know I can use LIKE or REGEXP. But these (already tried) ways are too slow. Can I introduce a fulltext index? Or should I add another helping table? Should I replace the special characters {, }, -, > to get words for the fulltext search? Or what else could I do?
The search works with some ten-thousand rows and I assume that I often get about one hundred hits.
This link should give you all the info you need regarding FULLTEXT indexes in MySQL.
MySQL dev site
The section that you will want to pay particular attention to is:
"Full-text searching is performed using MATCH() ... AGAINST syntax. MATCH() takes a comma-separated list that names the columns to be searched. 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 string value that is constant during query evaluation. This rules out, for example, a table column because that can differ for each row."
So in short, to answer your question you should see an improvement in query execution times by implementing a full text index on wide VARCHAR columns. Providing you are using a compatible storage engine ( InnoDB or MyISAM)
Also here is an example of how you can query the full text index and also an additional ID field as hinted in your question:
SELECT *
FROM table
WHERE MATCH (fieldlist) AGAINST ('search text here')
AND ( field2= '1234');
Let's say we have the following query:
SELECT *
FROM companies
WHERE name LIKE '%nited'
It returns
name
united
How do I write a query using MySQL's full-text search that will provide similar results?
Unfortunately you cannot do this using a MySQL full-text index. You cannot retrieve '*nited states' instantly from index because left characters are the most important part of the index. However, you can search 'United Sta*'.
// the only possible wildcard full-text search in MySQL
WHERE MATCH(column) AGAINST ('United Sta*' IN BOOLEAN MODE)
MySQL's full-text performs best when searching whole words in sentences - even that can suck at times. Otherwise, I'd suggest using an external full-text engine like Solr or Sphinx. I think Sphinx allows prefix and suffix wildcards, not sure about the others.
You could go back to MySQL's LIKE clause, but again, running queries like LIKE '%nited states' or LIKE '%nited Stat%', will also suffer on performance, as it can't use the index on the first few characters. 'United Sta%' and 'Unit%States' are okay as the index can be used against the first bunch of known characters.
Another quite major caveat using MySQL's full-text indexing is the stop-word list and minimum word length settings. For example, on a shared hosting environment, you will be limited to words greater than or equal to 4-characters. So searching 'Goo' to get 'Google' would fail. The stop-word list also disallows common words like 'and', 'maybe' and 'outside' - in-fact, there are 548 stop-words all together! Again, if not using shared hosting, these settings are relatively easily to modify, but if you are, then you will get annoyed with some of the default settings.
You can use MySQL's full-text index, but you must configure the parser to be the n-gram parser.
If your data is English (as opposed to Chinese or similar), you ought to also increase the ngram_token_size parameter to the minimum search term length you are willing to have. Otherwise, the search will be unacceptably slow.
You will also want to set innodb_ft_enable_stopword=0, otherwise an idiosyncrasy of how ngram stopword handling works will mean that many useful queries will return no results.
To explain why you must also increase ngram_token_size, you may think of this index as the following schema. MySQL then does a series of joins to find the results which match the search term:
CREATE TABLE fulltext_index
(
docid int(11) NOT NULL,
term char(2) NOT NULL,
PRIMARY KEY (docid, term),
INDEX term_idx (term)
);
The n-gram (2) parser breaks each word in your query into segments like se, eg, gm, me, en, nt, ts. For each of these n-grams, there are many results in English, so the index doesn't help much since it ends up iterating over everything anyway. Meanwhile, you can see how Chinese 随机的 would split into a much more useful 随机 and 机的. With n-gram size set to 4, the segments are segm, egme, gmen, ment, ents. These larger segments are much more likely to be unique, so each segment narrows down the search space significantly.
Disabling stopwords is also necessary because the ngram parser excludes all n-grams that contain any of the stopwords. For example, with an n-gram (4) parser, stopword will be parsed into stop, topw, opwr, pwor, and word:
stop will be excluded because it contains "to"
topw will be excluded because it contains "to"
opwr will be kept
pwor will be excluded because it contains "or"
word will be excluded because it contains "or"
Because these tokens are excluded from the index, a search for MATCH(name) AGAINST('stop' IN BOOLEAN MODE) would not return anything unless the stopwords mechanism is disabled before creating the index.
To answer your question,
set ngram_token_size to 3, 4, or whatever your minimum search term length is.
set innodb_ft_enable_stopword to 0 or OFF.
create the index with CREATE FULLTEXT INDEX companies_name_idx ON companies (name) WITH PARSER ngram;
SELECT * FROM companies WHERE MATCH(name) AGAINST('nited' IN BOOLEAN MODE);
This will also return results for nitedA, so you might want to further filter the results from there, if that's required for your application.
Im' trying to do a fulltext search with mysql, to match a string. The problem is that it's returning odd results in the first place.
For example, the string 'passat 2.0 tdi' :
AND MATCH (
records_veiculos.titulo, records_veiculos.descricao
)
AGAINST (
'passat 2.0 tdi' WITH QUERY EXPANSION
)
is returning this as the first result (the others are fine) :
Volkswagen Passat Variant 1.9 TDI- ANO 2003
wich is incorrect, since there's no "2.0" in this example.
What could it be?
edit: Also, since this will probably be a large database (expecting up to 500.000 records), will this search method be the best for itself, or would it be better to install any other search engine like Sphinx? Or in case it doesn't, how to show relevant results?
edit2: For the record, despite the question being marked as answered, the problem with the MySQL delimiters persists, so if anyone has a suggestion on how to escape delimiters, it would be appreciated and worth the 500 points at stake. The sollution I found to increase the resultset was to replace WITH QUERY EXPANSION with IN BOOLEAN MODE, using operators to force the engine to get the words I needed, like :
AND MATCH (
records_veiculos.titulo, records_veiculos.descricao
)
AGAINST (
'+passat +2.0 +tdi' IN BOOLEAN MODE
)
It didn't solve at all, but at least the relevance of the results as changed significantly.
From the MySQL documentation on Fulltext search:
"The FULLTEXT parser determines where words start and end by looking for certain delimiter characters; for example, “ ” (space), “,” (comma), and “.” (period)."
This means that the period is delimiting the 2 and 0. So it's not looking for '2.0'; it's looking for '2' and '0', and not finding it. WITH QUERY EXPANSION is probably causing relevant related words to show up, thus obviating the need for '2' and '0' to be individual words in the result rankings. A character minimum may also be being enforced.
By default I believe mysql only indexes and matches words with 4 or more characters. You could also try escaping the period? It might be ignored this or otherwise using it as a stop character.
What is the match rank that it returns for that? Does the match have to contain all "words" my understanding was it worked like Google and only needs to match some of the words.
Having said that, have a mind to the effect of adding WITH QUERY EXPANSION, that automatically runs a second search for "related" words, which may not be what you have typed, but which the fulltext engines deems probably related.
Relevant Documentation: http://dev.mysql.com/doc/refman/5.1/en/fulltext-query-expansion.html
The "." is what's matching on 2003 in your query results.
If you're going to do searches on 3 character text strings, you should set ft_min_word_len=3
in your mysql config, restart mysql. Otherwise, a search for "tdi" will return results with "TDI-" but not with just "TDI", because rows with "TDI-" will be indexed but "TDI" alone will not.
After making that config change, you'll have to rebuild your index on that table. (Warning: your index might be significantly larger now.)
I am trying to perform a search for users based on a full-text search.
SELECT * FROM users WHERE MATCH ( name ) AGAINST ( 'FDR' IN BOOLEAN MODE );
However the query yields no results. I can replace the search value with other strings and yield results.
I have even tried using a null stop word list with no success. The problem seems to with this particular string.
From dev.mysql.com/doc/refman/5.1/en/fulltext-fine-tuning.html
The default minimum value is four
characters; the default maximum is
version dependent. If you change
either value, you must rebuild your
FULLTEXT indexes.
The minimum and maximum lengths of
words to be indexed are defined by the
ft_min_word_len and ft_max_word_len
system variables.
Also see Server System Variables
If this article is still valid, then it's because MySQL fulltext indexing doesn't index words <= 3 characters long.