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Diffstat (limited to 'doc/src/sgml/pgtrgm.sgml')
| -rw-r--r-- | doc/src/sgml/pgtrgm.sgml | 28 |
1 files changed, 11 insertions, 17 deletions
diff --git a/doc/src/sgml/pgtrgm.sgml b/doc/src/sgml/pgtrgm.sgml index 5b630f203dd..e4c658145c4 100644 --- a/doc/src/sgml/pgtrgm.sgml +++ b/doc/src/sgml/pgtrgm.sgml @@ -1,4 +1,4 @@ -<!-- $PostgreSQL: pgsql/doc/src/sgml/pgtrgm.sgml,v 2.2 2007/12/10 05:32:51 tgl Exp $ --> +<!-- $PostgreSQL: pgsql/doc/src/sgml/pgtrgm.sgml,v 2.3 2010/07/29 19:34:40 petere Exp $ --> <sect1 id="pgtrgm"> <title>pg_trgm</title> @@ -136,27 +136,25 @@ <para> Example: - <programlisting> +<programlisting> CREATE TABLE test_trgm (t text); CREATE INDEX trgm_idx ON test_trgm USING gist (t gist_trgm_ops); - </programlisting> +</programlisting> or - <programlisting> +<programlisting> CREATE INDEX trgm_idx ON test_trgm USING gin (t gin_trgm_ops); - </programlisting> +</programlisting> </para> <para> At this point, you will have an index on the <structfield>t</> column that you can use for similarity searching. A typical query is - </para> - <programlisting> +<programlisting> SELECT t, similarity(t, '<replaceable>word</>') AS sml FROM test_trgm WHERE t % '<replaceable>word</>' ORDER BY sml DESC, t; - </programlisting> - <para> +</programlisting> This will return all values in the text column that are sufficiently similar to <replaceable>word</>, sorted from best match to worst. The index will be used to make this a fast operation even over very large data @@ -185,14 +183,12 @@ SELECT t, similarity(t, '<replaceable>word</>') AS sml <para> The first step is to generate an auxiliary table containing all the unique words in the documents: - </para> - <programlisting> +<programlisting> CREATE TABLE words AS SELECT word FROM ts_stat('SELECT to_tsvector(''simple'', bodytext) FROM documents'); - </programlisting> +</programlisting> - <para> where <structname>documents</> is a table that has a text field <structfield>bodytext</> that we wish to search. The reason for using the <literal>simple</> configuration with the <function>to_tsvector</> @@ -202,13 +198,11 @@ CREATE TABLE words AS SELECT word FROM <para> Next, create a trigram index on the word column: - </para> - <programlisting> +<programlisting> CREATE INDEX words_idx ON words USING gin(word gin_trgm_ops); - </programlisting> +</programlisting> - <para> Now, a <command>SELECT</command> query similar to the previous example can be used to suggest spellings for misspelled words in user search terms. A useful extra test is to require that the selected words are also of |