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Unlike Btree-based LIKE optimization, this works for non-left-anchored search patterns. The effectiveness of the search depends on how many trigrams can be extracted from the pattern. (The worst case, with no trigrams, degrades to a full-table scan, so this isn't a panacea. But it can be very useful.) Alexander Korotkov, reviewed by Jan Urbanski
73 lines
2.8 KiB
PL/PgSQL
73 lines
2.8 KiB
PL/PgSQL
--
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-- first, define the datatype. Turn off echoing so that expected file
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-- does not depend on contents of pg_tgrm.sql.
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--
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SET client_min_messages = warning;
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\set ECHO none
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\i pg_trgm.sql
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\set ECHO all
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RESET client_min_messages;
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select show_trgm('');
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select show_trgm('(*&^$@%@');
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select show_trgm('a b c');
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select show_trgm(' a b c ');
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select show_trgm('aA bB cC');
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select show_trgm(' aA bB cC ');
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select show_trgm('a b C0*%^');
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select similarity('wow','WOWa ');
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select similarity('wow',' WOW ');
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CREATE TABLE test_trgm(t text);
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\copy test_trgm from 'data/trgm.data
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select t,similarity(t,'qwertyu0988') as sml from test_trgm where t % 'qwertyu0988' order by sml desc, t;
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select t,similarity(t,'gwertyu0988') as sml from test_trgm where t % 'gwertyu0988' order by sml desc, t;
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select t,similarity(t,'gwertyu1988') as sml from test_trgm where t % 'gwertyu1988' order by sml desc, t;
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select t <-> 'q0987wertyu0988', t from test_trgm order by t <-> 'q0987wertyu0988' limit 2;
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create index trgm_idx on test_trgm using gist (t gist_trgm_ops);
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set enable_seqscan=off;
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select t,similarity(t,'qwertyu0988') as sml from test_trgm where t % 'qwertyu0988' order by sml desc, t;
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select t,similarity(t,'gwertyu0988') as sml from test_trgm where t % 'gwertyu0988' order by sml desc, t;
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select t,similarity(t,'gwertyu1988') as sml from test_trgm where t % 'gwertyu1988' order by sml desc, t;
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explain (costs off)
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select t <-> 'q0987wertyu0988', t from test_trgm order by t <-> 'q0987wertyu0988' limit 2;
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select t <-> 'q0987wertyu0988', t from test_trgm order by t <-> 'q0987wertyu0988' limit 2;
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drop index trgm_idx;
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create index trgm_idx on test_trgm using gin (t gin_trgm_ops);
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set enable_seqscan=off;
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select t,similarity(t,'qwertyu0988') as sml from test_trgm where t % 'qwertyu0988' order by sml desc, t;
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select t,similarity(t,'gwertyu0988') as sml from test_trgm where t % 'gwertyu0988' order by sml desc, t;
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select t,similarity(t,'gwertyu1988') as sml from test_trgm where t % 'gwertyu1988' order by sml desc, t;
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create table test2(t text);
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insert into test2 values ('abcdef');
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insert into test2 values ('quark');
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create index test2_idx_gin on test2 using gin (t gin_trgm_ops);
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set enable_seqscan=off;
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explain (costs off)
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select * from test2 where t like '%BCD%';
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explain (costs off)
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select * from test2 where t ilike '%BCD%';
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select * from test2 where t like '%BCD%';
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select * from test2 where t like '%bcd%';
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select * from test2 where t ilike '%BCD%';
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select * from test2 where t ilike 'qua%';
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drop index test2_idx_gin;
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create index test2_idx_gist on test2 using gist (t gist_trgm_ops);
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set enable_seqscan=off;
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explain (costs off)
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select * from test2 where t like '%BCD%';
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explain (costs off)
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select * from test2 where t ilike '%BCD%';
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select * from test2 where t like '%BCD%';
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select * from test2 where t like '%bcd%';
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select * from test2 where t ilike '%BCD%';
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select * from test2 where t ilike 'qua%';
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