问题
I wonder if the following is possible with fts(3/4) for SQLite. I created a table with some data using fts3.
If i for example search for e* i get everything that starts with ^e But can i also search the index/catalog for the specific words that starts with e?
So that i only get the results of that words back like; elliot, elo,eehh.
回答1:
http://www.sqlite.org/fts3.html#section_3
SELECT * FROM docs WHERE docs MATCH 'lin*';
Will return the docs that contain a word starting with "lin". You only want the words that match, not the context? Maybe the "snippets" feature will help you. And you may find this thread of interest:
http://www.mail-archive.com/sqlite-users@sqlite.org/msg49345.html
回答2:
The FTS engine provides that information via the offsets virtual function.
SELECT offsets(docs) FROM docs WHERE docs MATCH 'e*';
As the documentation says:
For a SELECT query that uses the full-text index, the offsets() function returns a text value containing a series of space-separated integers. For each term in each phrase match of the current row, there are four integers in the returned list. Each set of four integers is interpreted as follows:
- The column number that the term instance occurs in (0 for the leftmost column of the FTS table, 1 for the next leftmost, etc.).
- The term number of the matching term within the full-text query expression. Terms within a query expression are numbered starting from 0 in the order that they occur.
- The byte offset of the matching term within the column.
- The size of the matching term in bytes.
How to extract that information is up to you and how you integrate your code with SQLite.
回答3:
the documentation of the snippet function is rather vague regarding its 6th parameter because the algorithm uses a best-score approach to find the snippet.
Nevertheless in my application i get a clean extract of the original terms I am looking for with the request :
select snippet(docs,'','','', -1, 1) from docs where docs match 'e*';
It may help in your case ; this in-database solution helped me because i didn't want to extract the terms in code located outside of the db. It works if you are searching for single words (no space, OR, .. in the MATCH query)
来源：https://stackoverflow.com/questions/4519854/sqlite-full-text-search-catalog