# groonga - An open-source fulltext search engine and column store.

- 日本語

# 7.15.21. `snippet_html`

## 7.15.21.1. Summary

This function extracts snippets of target text around search keywords (`KWIC`. `KeyWord In Context`).

The snippets are prepared for embedding HTML. Special characters such as `<` and `>` are escapsed as `&lt;` and `&gt;`. Keyword is surrounded with `<span class="keyword">` and `</span>`. For example, a snippet of `I am a groonga user. <3` for keyword `groonga` is `I am a <span class="keyword">groonga</span> user. &lt;3`.

This function is a HTML specific version of snippet. Generally, this function is enough for normal Web application use.

## 7.15.21.2. Syntax

`snippet_html` has only one parameter:

    snippet_html(column)

## 7.15.21.3. Usage

Here are a schema definition and sample data to show usage.

Execution example:

    table_create Documents TABLE_NO_KEY
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_create Documents content COLUMN_SCALAR Text
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    table_create Terms TABLE_PAT_KEY ShortText --default_tokenizer TokenBigram  --normalizer NormalizerAuto
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_create Terms documents_content_index COLUMN_INDEX|WITH_POSITION Documents content
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    load --table Documents
    [
    ["content"],
    ["Groonga is a fast and accurate full text search engine based on inverted index. One of the characteristics of groonga is that a newly registered document instantly appears in search results. Also, groonga allows updates without read locks. These characteristics result in superior performance on real-time applications."],
    ["Groonga is also a column-oriented database management system (DBMS). Compared with well-known row-oriented systems, such as MySQL and PostgreSQL, column-oriented systems are more suited for aggregate queries. Due to this advantage, groonga can cover weakness of row-oriented systems."]
    ]
    # [[0, 1337566253.89858, 0.000355720520019531], 2]

`snippet_html` can be used in only `--output_columns` in select.

You also need to specify `--query` and/or `--filter`. Keywords are extracted from `--query` and `--filter` arguments.

The following example uses `--query "fast performance"`. In this case, `fast` and `performance` are used as keywords.

Execution example:

    select Documents --output_columns "snippet_html(content)" --command_version 2 --match_columns content --query "fast performance"
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         1
    #       ],
    #       [
    #         [
    #           "snippet_html",
    #           null
    #         ]
    #       ],
    #       [
    #         [
    #           "Groonga is a <span class=\"keyword\">fast</span> and accurate full text search engine based on inverted index. One of the characteristics of groonga is that a newly registered document instantly appears in search results. Also, gro",
    #           "onga allows updates without read locks. These characteristics result in superior <span class=\"keyword\">performance</span> on real-time applications."
    #         ]
    #       ]
    #     ]
    #   ]
    # ]

`--query "fast performance"` matches to only the first record’s content. `snippet_html(content)` extracts two text parts that include the keywords `fast` or `performance` and surrounds the keywords with `<span class="keyword">` and `</span>`.

The max number of text parts is 3. If there are 4 or more text parts that include the keywords, only the leading 3 parts are only used.

The max size of a text part is 200byte. The unit is bytes not characters. The size doesn’t include inserted `<span class="keyword">` and `</span>`.

Both the max number of text parts and the max size of a text part aren’t customizable.

If you want to customize them, you need to use snippet instead of this function.

You can specify string literal instead of column.

Execution example:

    select Documents --output_columns 'snippet_html("Groonga is very fast fulltext search engine.")' --command_version 2 --match_columns content --query "fast performance"
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         1
    #       ],
    #       [
    #         [
    #           "snippet_html",
    #           null
    #         ]
    #       ],
    #       [
    #         [
    #           "Groonga is very <span class=\"keyword\">fast</span> fulltext search engine."
    #         ]
    #       ]
    #     ]
    #   ]
    # ]

## 7.15.21.4. Return value

This function returns an array of string or `null`. If This function can’t find any snippets, it returns `null`.

An element of array is a snippet:

    [SNIPPET1, SNIPPET2, SNIPPET3]

A snippet includes one or more keywords. The max byte size of a snippet except open tag and close tag is 200byte. The unit isn’t the number of characters.

Open tag is `<span class="keyword">` and close tag is `</span>`.

The array size is larger than or equal to 1 and less than or equal to 3.

If you want to customize the max byte size of snippet and/or the max number of snippets, use snippet instead.

## 7.15.21.5. See also

- snippet

- select