Postgres Full-Text Search with Hyphen and Numerals - postgresql

Question

I have observed what seems to me an odd behavior of Postgres' to_tsvector function.
SELECT to_tsvector('english', 'abc-xyz');
returns
'abc':2 'abc-xyz':1 'xyz':3
However,
SELECT to_tsvector('english', 'abc-001');
returns
'-001':2 'abc':1
Why not something like this?
'abc':2 'abc-001':1 '001':3
And what should I do to be able to search by the numeric portion alone, without the hyphen?

Answer 1

Seems the text search parser identifies the hyphen followed by digits to be the sign of a signed integer. Debug with ts_debug():
SELECT * FROM ts_debug('english', 'abc-001');
alias | description | token | dictionaries | dictionary | lexemes
-----------+-----------------+-------+--------------+------------+---------
asciiword | Word, all ASCII | abc | {simple} | simple | {abc}
int | Signed integer | -001 | {simple} | simple | {-001}
Other text search configurations (like 'simple' instead of 'english') won't help as the parser itself is "at fault" here (debatable).
A simple way around it (other than modifying the parser, which I never tried) would to pre-process strings and replace hyphens with m-dash (—) or just blanks to make sure those are identified as "Space symbols". (Actual signed integers lose their negative sign in the process.)
SELECT to_tsvector('english', translate('abc-001', '-', '—'))
## to_tsquery ('english', '001'); -- true now
db<>fiddle here

Answer 2

This can be circumvented with PG13's dict-int addon's absval option. See the official documentation.
But in case you're stuck with an earlier PG version, here's the generalized version of a "number or negative number" workaround in a query.
select regexp_replace($$'test' & '1':* & '2'$$::tsquery::text,
'''([.\d]+''(:\*)?)', '(''\1 | ''-\1)', 'g')::tsquery;
This results in:
'test' & ( '1':* | '-1':* ) & ( '2' | '-2' )
It replaces lexemes that look like positive numbers with "number or negative number" kind of subqueries.
The double cast ::tsquery::text is just there to show how you would pass a tsquery casted to text.
Note that it handles prefix matching numeric lexemes as well.