On Mon, May 30, 2016 at 1:53 PM, Volker Boehm <vol...@vboehm.de> wrote:
> > 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.
