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

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# 7.12.7. highlight_html

Caution

This feature is experimental. API will be changed.

## 7.12.7.1. Summary

`highlight_html` tags target text. It can use to highlight the search keywords. The tagged text 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 tagged text of `I am a groonga user. <3` for keyword `groonga` is `I am a <span class="keyword">groonga</span> user. &lt;3`.

## 7.12.7.2. Syntax

`highlight_html` has only one parameter:

    highlight_html(column)

## 7.12.7.3. Usage

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

Execution example:

    table_create Entries TABLE_NO_KEY
    # [[0,1407692435.35498,0.0364797115325928],true]
    column_create Entries body COLUMN_SCALAR ShortText
    # [[0,1407692435.39156,0.0256640911102295],true]
    table_create Terms TABLE_PAT_KEY ShortText --default_tokenizer TokenBigram --normalizer NormalizerAuto
    # [[0,1407692435.423,0.0274741649627686],true]
    column_create Terms document_index COLUMN_INDEX|WITH_POSITION Entries body
    # [[0,1407692435.45051,0.0534985065460205],true]
    load --table Entries
    [
    {"body": "Mroonga is a ＭｙＳＱＬ storage engine based on Groonga. <b>Rroonga</b> is a Ruby binding of Groonga."}
    ]
    # [[0,1407692435.50406,0.378907442092896],1]

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

`highlight_html` requires Groonga 4.0.5 or later.

`highlight_html` requires コマンドバージョン 2 or later.

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

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

Execution example:

    select Entries --output_columns --match_columns body --query 'groonga mysql' --output_columns 'highlight_html(body)' --command_version 2
    # [
    #   [
    #     0,
    #     1407692444.86092,
    #     0.00188779830932617
    #   ],
    #   [
    #     [
    #       [
    #         1
    #       ],
    #       [
    #         [
    #           "highlight_html",
    #           "null"
    #         ]
    #       ],
    #       [
    #         "Mroonga is a <span class=\"keyword\">ＭｙＳＱＬ</span> storage engine based on <span class=\"keyword\">Groonga</span>. &lt;b&gt;Rroonga&lt;/b&gt; is a Ruby binding of <span class=\"keyword\">Groonga</span>."
    #       ]
    #     ]
    #   ]
    # ]

The text are scanned by the keywords for tagging after they are normalized by `NormalizerAuto` normalizer.

`--query "groonga mysql"` matches to only the first record's body. `highlight_html(body)` surrounds the keywords `groonga` or `mysql` contained in the text with `<span class="keyword">` and `</span>`.

You can specify string literal instead of column.

Execution example:

    select Entries --output_columns 'highlight_html("Groonga is very fast fulltext search engine.")' --command_version 2 --match_columns body --query "groonga"
    # [
    #   [
    #     0,
    #     1407693081.99183,
    #     0.000126123428344727
    #   ],
    #   [
    #     [
    #       [
    #         1
    #       ],
    #       [
    #         [
    #           "highlight_html",
    #           "null"
    #         ]
    #       ],
    #       [
    #         "<span class=\"keyword\">Groonga</span> is very fast fulltext search engine."
    #       ]
    #     ]
    #   ]
    # ]

## 7.12.7.4. Parameters

There is only one parameter `column` .

### 7.12.7.4.1. `column`

It specifies a column of the table.

## 7.12.7.5. Return value

`highlight_html` returns a tagged string or `null`. If `highlight_html` can't find any keywords, it returns `null`.

## 7.12.7.6. See also

- select
- highlight_full