bjorn@eventmy.com writes:
> Working correctly, no results:
> SELECT ts_rank(to_tsvector('lets eat a cat'), ('fat & bat | rat'::tsquery &&
> 'cat'::tsquery));
> ts_rank
> ---------
> 1e-20
> (1 row)
> Should also yield no results:
> SELECT ts_rank(to_tsvector('lets eat a fat cat'), ('fat & bat |
> rat'::tsquery && 'cat'::tsquery));
> ts_rank
> -----------
> 0.0991032
> (1 row)
> Is this intended behavior?
Don't see what you find surprising about it? ts_rank() is documented as
Ranks vectors based on the frequency of their matching lexemes.
The first example has one lexeme that matches the query's lexemes,
the second has two. It should get a higher ranking.
If you want to know whether the tsvector formally matches the query,
you should be applying the @@ operator. ts_rank() is not a binary
yes/no thing, it's trying to identify stuff that is more or less
relevant to the query's terms. At least from the documentation,
I'd suspect it pays no attention to the operators in the query.
In short: the intended use of ts_rank() is for sorting values that
have already passed an @@ match. It's not a substitute for @@.
regards, tom lane
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