PostgreSQL , 文本相似 , pg_similarity , pg_trgm , rum , fuzzymatch gin , smlar
文本相似算法，结合PostgreSQL的开放索引框架GIN，可以实现各种相似算法的文本高效检索。
PostgreSQL中常见的文本相似搜索插件：rum, pg_trgm, fuzzymatch, pg_similarity, smlar。
其中pg_similarity支持的算法达到了17种。
Introduction
pg_similarity is an extension to support similarity queries on PostgreSQL.
The implementation is tightly integrated in the RDBMS in the sense that it defines operators so instead of the traditional operators (= and <>) you can use ~~~ and ! (any of these operators represents a similarity function).
pg_similarity has three main components:
Functions:
a set of functions that implements similarity algorithms available in the literature.
These functions can be used as UDFs and, will be the base for implementing the similarity operators;
Operators:
a set of operators defined at the top of similarity functions.
They use similarity functions to obtain the similarity threshold and, compare its value to a user-defined threshold to decide if it is a match or not;
Session Variables:
a set of variables that store similarity function parameters. Theses variables can be defined at run time.
L1 Distance (as known as City Block or Manhattan Distance);Cosine Distance;Dice Coefficient;Euclidean Distance;Hamming Distance;Jaccard Coefficient;Jaro Distance;Jaro-Winkler Distance;Levenshtein Distance;Matching Coefficient;Monge-Elkan Coefficient;Needleman-Wunsch Coefficient;Overlap Coefficient;Q-Gram Distance;Smith-Waterman Coefficient;Smith-Waterman-Gotoh Coefficient;Soundex Distance.用法如下
AlgorithmFunctionOperatorUse Index?ParametersL1 Distanceblock(text, text) returns float8~++yespg_similarity.block_tokenizer (enum) pg_similarity.block_threshold (float8) pg_similarity.block_is_normalized (bool)Cosine Distancecosine(text, text) returns float8~##yespg_similarity.cosine_tokenizer (enum) pg_similarity.cosine_threshold (float8) pg_similarity.cosine_is_normalized (bool)Dice Coefficientdice(text, text) returns float8~-~yespg_similarity.dice_tokenizer (enum) pg_similarity.dice_threshold (float8) pg_similarity.dice_is_normalized (bool)Euclidean Distanceeuclidean(text, text) returns float8~!!yespg_similarity.euclidean_tokenizer (enum) pg_similarity.euclidean_threshold (float8) pg_similarity.euclidean_is_normalized (bool)Hamming Distancehamming(bit varying, bit varying) returns float8 hamming_text(text, text) returns float8~@~nopg_similarity.hamming_threshold (float8) pg_similarity.hamming_is_normalized (bool)Jaccard Coefficientjaccard(text, text) returns float8~??yespg_similarity.jaccard_tokenizer (enum) pg_similarity.jaccard_threshold (float8) pg_similarity.jaccard_is_normalized (bool)Jaro Distancejaro(text, text) returns float8~%%nopg_similarity.jaro_threshold (float8) pg_similarity.jaro_is_normalized (bool)Jaro-Winkler Distancejarowinkler(text, text) returns float8~@@nopg_similarity.jarowinkler_threshold (float8) pg_similarity.jarowinkler_is_normalized (bool)Levenshtein Distancelev(text, text) returns float8~==nopg_similarity.levenshtein_threshold (float8) pg_similarity.levenshtein_is_normalized (bool)Matching Coefficientmatchingcoefficient(text, text) returns float8~^^yespg_similarity.matching_tokenizer (enum) pg_similarity.matching_threshold (float8) pg_similarity.matching_is_normalized (bool)Monge-Elkan Coefficientmongeelkan(text, text) returns float8~||nopg_similarity.mongeelkan_tokenizer (enum) pg_similarity.mongeelkan_threshold (float8) pg_similarity.mongeelkan_is_normalized (bool)Needleman-Wunsch Coefficientneedlemanwunsch(text, text) returns float8~#~nopg_similarity.nw_threshold (float8) pg_similarity.nw_is_normalized (bool)Overlap Coefficientoverlapcoefficient(text, text) returns float8~**yespg_similarity.overlap_tokenizer (enum) pg_similarity.overlap_threshold (float8) pg_similarity.overlap_is_normalized (bool)Q-Gram Distanceqgram(text, text) returns float8~~~yespg_similarity.qgram_threshold (float8) pg_similarity.qgram_is_normalized (bool)Smith-Waterman Coefficientsmithwaterman(text, text) returns float8~=~nopg_similarity.sw_threshold (float8) pg_similarity.sw_is_normalized (bool)Smith-Waterman-Gotoh Coefficientsmithwatermangotoh(text, text) returns float8~!~nopg_similarity.swg_threshold (float8) pg_similarity.swg_is_normalized (bool)Soundex Distancesoundex(text, text) returns float8~*~nohttp://pgsimilarity.projects.pgfoundry.org/
https://github.com/eulerto/pg_similarity
https://www.pgcon.org/2009/schedule/attachments/108_pg_similarity.pdf
http://www.sigaev.ru/git/gitweb.cgi?p=smlar.git;a=summary
https://github.com/postgrespro/rum
https://www.postgresql.org/docs/9.6/static/fuzzystrmatch.html
https://www.postgresql.org/docs/9.6/static/pgtrgm.html
