diff --git a/contrib/pg_trgm/trgm_op.c b/contrib/pg_trgm/trgm_op.c
index 368e7c8941..32adecc9b8 100644
--- a/contrib/pg_trgm/trgm_op.c
+++ b/contrib/pg_trgm/trgm_op.c
@@ -456,7 +456,7 @@ iterate_word_similarity(int *trg2indexes,
lastpos[trgindex] = i;
}
- /* Adjust lower bound if this trigram is present in required substring */
+ /* Adjust upper bound if this trigram is present in required substring */
if (found[trgindex])
{
int prev_lower,
@@ -473,7 +473,7 @@ iterate_word_similarity(int *trg2indexes,
smlr_cur = CALCSML(count, ulen1, ulen2);
- /* Also try to adjust upper bound for greater similarity */
+ /* Also try to adjust lower bound for greater similarity */
tmp_count = count;
tmp_ulen2 = ulen2;
prev_lower = lower;
diff --git a/doc/src/sgml/pgtrgm.sgml b/doc/src/sgml/pgtrgm.sgml
index 775a7b8be7..2613c7a3d5 100644
--- a/doc/src/sgml/pgtrgm.sgml
+++ b/doc/src/sgml/pgtrgm.sgml
@@ -99,12 +99,10 @@
real
- Returns a number that indicates how similar the first string
- to the most similar word of the second string. The function searches in
- the second string a most similar word not a most similar substring. The
- range of the result is zero (indicating that the two strings are
- completely dissimilar) to one (indicating that the first string is
- identical to one of the words of the second string).
+ Returns a number that indicates the greatest similarity between
+ the set of trigrams in the first string and any continuous extent
+ of an ordered set of trigrams in the second string. For details, see
+ the explanation below.
@@ -131,6 +129,34 @@
+
+ Consider the following example:
+
+
+# SELECT word_similarity('word', 'two words');
+ word_similarity
+-----------------
+ 0.8
+(1 row)
+
+
+ In the first string, the set of trigrams is
+ {" w"," wo","ord","wor","rd "}.
+ In the second string, the ordered set of trigrams is
+ {" t"," tw",two,"wo "," w"," wo","wor","ord","rds", ds "}.
+ The most similar extent of an ordered set of trigrams in the second string
+ is {" w"," wo","wor","ord"}, and the similarity is
+ 0.8.
+
+
+
+ This function returns a value that can be approximately understood as the
+ greatest similarity between the first string and any substring of the second
+ string. However, this function does not add padding to the boundaries of
+ the extent. Thus, a whole word match gets a higher score than a match with
+ a part of the word.
+
+
pg_trgm Operators
@@ -156,10 +182,11 @@
text> <% text>
boolean
- Returns true> if its first argument has the similar word in
- the second argument and they have a similarity that is greater than the
- current word similarity threshold set by
- pg_trgm.word_similarity_threshold> parameter.
+ Returns true if the similarity between the trigram
+ set in the first argument and a continuous extent of an ordered trigram
+ set in the second argument is greater than the current word similarity
+ threshold set by pg_trgm.word_similarity_threshold
+ parameter.
@@ -302,10 +329,11 @@ SELECT t, word_similarity('word>', t) AS sml
WHERE 'word>' <% t
ORDER BY sml DESC, t;
- This will return all values in the text column that have a word
- which sufficiently similar to word>, sorted from best
- match to worst. The index will be used to make this a fast operation
- even over very large data sets.
+ This will return all values in the text column for which there is a
+ continuous extent in the corresponding ordered trigram set that is
+ sufficiently similar to the trigram set of word,
+ sorted from best match to worst. The index will be used to make this
+ a fast operation even over very large data sets.