On Fri, May 31, 2013 at 11:16 AM, Amit Langote <amitlangot...@gmail.com> wrote: > On Fri, May 31, 2013 at 4:25 AM, Alexander Korotkov > <aekorot...@gmail.com> wrote: >> On Thu, May 30, 2013 at 12:49 PM, Sawada Masahiko <sawada.m...@gmail.com> >> wrote: >>> >>> following emails are discussed about partial match of pg_trgm. I hope >>> will this help. >>> >>> <http://www.postgresql.org/message-id/cahgqgwfjshvv2ngme19wdtw9tefw_w7h2ns4e+yysjkb9wd...@mail.gmail.com> >>> as you may know, if search string contains multibyte characters >>> trigram key is converted to CRC of 4 byte and it is used as key. >>> (but only use upper 3 byte from CRC) >>> so we can do partial matching if KEEPONLYALNUM is enabled. >> >> >> Please, read the further discussion on that thread. We can't do partial >> matching because of CRC independently of KEEPONLYALNUM. >> > > Also, a few more questions: > > 1) When building a trgm index, are there any differences for > multi-byte character strings. For example, would a 2 character > Japanese string (multi-byte offcourse) produce exactly 3 trigrams to > be stored in the index which would later be used while look-up?
in above case a 2 character multibyte string produce 3 trigrams of CRC. (because these was larger than 3 byte) and these are used while look-up. > 2) And if that is so, is there problem in gin_extract_query_trgm(), > that is while generating trigrams from a query search term that causes > trigrams (stored in the index if answer to (1) is yes) NOT to be used > in such a partial matching case? it means that we can't use trigrams in case of partial matching because trigrams (stored in index) are converted to different value(CRC). right? Regards, -- ------- Sawada Masahiko -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
