Re: Grouping By Similarity (using pg_trgm)?

On Thu, May 14, 2015 at 11:58 AM, Cory Tucker <cory.tucker@gmail.com> wrote:

[pg version 9.3 or 9.4]

Suppose I have a simple table:

create table data (

  my_value  TEXT NOT NULL

);

CREATE INDEX idx_my_value ON data USING gin(my_value gin_trgm_ops);

Now I would like to essentially do group by to get a count of all the values that are sufficiently similar.  I can do it using something like a CROSS JOIN to join the table on itself, but then I still am getting all the rows with duplicate counts.  

Is there a way to do a group by query and only return a single "my_value" column and a count of the number of times other values are similar while also not returning the included similar values in the output, too?

​Concept below - not bothering to lookup the functions/operators for pg_trgm:

SELECT my_value_src, count(*)

FROM (SELECT my_value AS my_value_src FROM data) src

JOIN (SELECT my_value AS my_value_compareto FROM data) comparedto

ON ( func(my_value_src, my_value_compareto) < # )

GROUP BY my_value_src

​David J.