5.5.6. mroonga_snippet() — Mroonga vmrn_version documentation

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# 5.5.6. `mroonga_snippet()`

Added in version 2.07.

## 5.5.6.1. Summary

`mroonga_snippet()` UDF provides functionality to get keyword in context.

## 5.5.6.2. Syntax

`mroonga_snippet()` has required parameter and optional parameter:

    mroonga_snippet(document,
                    max_length,
                    max_count,
                    encoding,
                    skip_leading_spaces,
                    html_escape,
                    snippet_prefix,
                    snippet_suffix,
                    word1, word1_prefix, word1_suffix,
                    ...,
                    [wordN, wordN_prefix, wordN_suffix])

## 5.5.6.3. Usage

There is a case that you want to extract keyword and surrounding text as a search results.

Snippet means ‘keyword and surrounding text’. It is called ‘Keyword in context’.

`mroonga_snippet()` function provides the way to get snippet from search results.

You can use `mroonga_snippet()` UDF in storage mode and wrapper mode.

`mroonga_snippet()` function is included in Mroonga as a User-Defined Function (UDF), but if you have not yet register it in MySQL by CREATE FUNCTION, you need to invoke the following SQL for defining a function.

    mysql> CREATE FUNCTION mroonga_snippet RETURNS STRING SONAME 'ha_mroonga.so';

`mroonga_snippet()` function is useful for searching the text which contains keyword and associated one by using MATCH .. AGAINST syntax.

Imagine searching the document which contains ‘fulltext’ as a keyword. Assume that some keyword such as ‘MySQL’ and ‘search’ are associated with ‘fulltext’.

`mroonga_snippet()` function meets above.

Here is the schema definition for execution examples(storage mode):

    CREATE TABLE `snippet_test` (
      `id` int(11) NOT NULL,
      `text` text,
      PRIMARY KEY (`id`),
      FULLTEXT KEY `text` (`text`)
    ) ENGINE=mroonga DEFAULT CHARSET=utf8

Here is the schema definition for execution examples(wrapper mode):

    CREATE TABLE `snippet_test` (
      `id` int(11) NOT NULL,
      `text` text,
      PRIMARY KEY (`id`),
      FULLTEXT KEY `text` (`text`)
    ) ENGINE=mroonga COMMENT 'engine = "innodb"' DEFAULT CHARSET=utf8

Here is the sample data for execution examples:

    INSERt INTO snippet_test (id, text) VALUES (1, 'An open-source fulltext search engine and column store.');
    INSERT INTO snippet_test (id, text) VALUES (2, 'An open-source storage engine for fast fulltext search with MySQL.');
    INSERT INTO snippet_test (id, text) VALUES (3, 'Tritonn is a patched version of MySQL that supports better fulltext search function with Senna.');

Here is the results of execution examples:

    mysql> SELECT * FROM snippet_test;
    +----+-------------------------------------------------------------------------------------------------+
    | id | text                                                                                            |
    +----+-------------------------------------------------------------------------------------------------+
    |  1 | An open-source fulltext search engine and column store.                                         |
    |  2 | An open-source storage engine for fast fulltext search with MySQL.                              |
    |  3 | Tritonn is a patched version of MySQL that supports better fulltext search function with Senna. |
    +----+-------------------------------------------------------------------------------------------------+
    3 rows in set (0.00 sec)

    mysql> SELECT id, text, mroonga_snippet(text, 8, 2, 'ascii_general_ci', 1, 1, '...', '...<br>', 'fulltext', '<span class="w1">', '</span>', 'MySQL', '<span class="w2">', '</span>', 'search', '<span calss="w3">', '</span>') FROM snippet_test WHERE MATCH(text) AGAINST ('+fulltext' IN BOOLEAN MODE);
    +----+-------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
    | id | text                                                                                            | mroonga_snippet(text, 8, 2, 'ascii_general_ci', 1, 1, '...', '...<br>', 'fulltext', '<span class="w1">', '</span>', 'MySQL', '<span class="w2">', '</span>', 'search', '<span calss="w3">', '</span>') |
    +----+-------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
    |  1 | An open-source fulltext search engine and column store.                                         | ...<span class="w1">fulltext</span>...<br>... <span calss="w3">search</span> ...<br>                                                                                                                   |
    |  2 | An open-source storage engine for fast fulltext search with MySQL.                              | ...<span class="w1">fulltext</span>...<br>... <span calss="w3">search</span> ...<br>                                                                                                                   |
    |  3 | Tritonn is a patched version of MySQL that supports better fulltext search function with Senna. | ...f <span class="w2">MySQL</span> ...<br>...<span class="w1">fulltext</span>...<br>                                                                                                                   |
    +----+-------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
    3 rows in set (0.00 sec)

The keyword ‘fulltext’ and associated keyword ‘MySQL’ and ‘search’ has been extracted.

## 5.5.6.4. Parameters

### 5.5.6.4.1. Required parameters

There are many required parameters.

#### 5.5.6.4.1.1. `document`

The column name or string value is required.

#### 5.5.6.4.1.2. `max_length`

The max length of snippet (bytes) is required.

#### 5.5.6.4.1.3. `max_count`

The max elements of snippets (N word) is required.

#### 5.5.6.4.1.4. `encoding`

The encoding of document is required. You can specify the value of encoding such as ‘ascii_general_ci’, ‘cp932_japanese_ci’, ‘eucjpms_japanese_ci’ and so on.

#### 5.5.6.4.1.5. `skip_leading_spaces`

Specify whether skip leading spaces or not. Specify the value 1 for skipping leading spaces, 0 for not.

#### 5.5.6.4.1.6. `html_escape`

HTML escape is enabled or not. Specify the value 1 for enabling HTML escape, 0 for not.

#### 5.5.6.4.1.7. `prefix`

The start text of snippet.

#### 5.5.6.4.1.8. `suffix`

The end text of snippet.

### 5.5.6.4.2. Optional parameters

There is one optional group parameter, `wordN` related prefix and suffix.

#### 5.5.6.4.2.1. `wordN`

Specify any word.

#### 5.5.6.4.2.2. `wordN_prefix`

It is the start text of wordN.

#### 5.5.6.4.2.3. `wordN_suffix`

It is the end text of wordN.

## 5.5.6.5. Return value

It returns snippet string.