The reason for using the similarity function in place of the '%'-operator is that I want to use different similarity values in one query:
select name, street, zip, city
from addresses
where name % $1
and street % $2
and (zip % $3 or city % $4)
or similarity(name, $1) > 0.8
which means: take all addresses where name, street, zip and city have little similarity _plus_ all addresses where the name matches very good.
The only way I found, was to create a temporary table from the first query, change the similarity value with set_limit() and then select the second query UNION the temporary table.
Is there a more elegant and straight forward way to achieve this result?
Not that I can envision.
You are forced into using an operator due to our index implementation.
You are thus forced into using a GUC to control the parameter that the index scanning function uses to compute true/false.
A GUC can only take on a single value within a given query - well, not quite true[1] but the exception doesn't seem like it will help here.
Th
us you are consigned to
using two queries.
*A functional index doesn't work since the second argument is query specific
[1] When defining a function you can attach a "SET" clause to it; commonly used for search_path but should work with any GUC. If you could wrap the operator comparison into a custom function you could use this capability. It also would require a function that would take the threshold as a value - the extension only provides variations that use the GUC.
I don't think this will use the index even if it compiles (not tested):
CREATE FUNCTION similarity_80(col, val)
RETURNS boolean
SET similarity_threshold = 0.80
LANGUAGE sql
AS $$
SELECT col % val;
$$;
David J.
