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.. -*- rst -*-
.. groonga-command
.. database: string_substring
``string_substring``
====================
.. versionadded:: 6.0.7
Summary
-------
``string_substring`` extracts a substring of a string by position.
To enable this function, register ``functions/string`` plugin by following the command::
plugin_register functions/string
Syntax
------
``string_substring`` requires two to four parameters.
::
string_substring(target, nth[, options])
string_substring(target, nth, length[, options])
``options`` uses the following format. All of key-value pairs are optional::
{
"default_value": default_value
}
Usage
-----
Here are a schema definition and sample data to show usage.
Sample schema:
.. groonga-command
.. include:: ../../example/reference/functions/string_substring/usage_setup_schema.log
.. plugin_register functions/string
.. table_create Memos TABLE_HASH_KEY ShortText
Sample data:
.. groonga-command
.. include:: ../../example/reference/functions/string_substring/usage_setup_data.log
.. load --table Memos
.. [
.. {"_key": "Groonga"}
.. ]
Here is a simple example.
.. groonga-command
.. include:: ../../example/reference/functions/string_substring/usage_number.log
.. select Memos --output_columns '_key, string_substring(_key, 2, 3)'
In the following example, specifying the negative value for ``nth``.
.. groonga-command
.. include:: ../../example/reference/functions/string_substring/usage_negative.log
.. select Memos --output_columns '_key, string_substring(_key, -3, 2)'
In the following example, specifying the default value.
.. groonga-command
.. include:: ../../example/reference/functions/string_substring/usage_default.log
.. select Memos --output_columns '_key, string_substring(_key, 50, 1, { "default_value" : "default" })'
You can specify string literal instead of column.
.. groonga-command
.. include:: ../../example/reference/functions/string_substring/usage_string_literal.log
.. select Memos --output_columns 'string_substring("Groonga", 2, 3)'
Parameters
----------
Required parameters
^^^^^^^^^^^^^^^^^^^
``target``
~~~~~~~~~~
Specify a string literal or a string type column.
``nth``
~~~~~~~
Specify a 0-based index number of charactors where to start the extraction from ``target``.
If you specify a negative value, it counts from the end of ``target``.
Optional parameters
^^^^^^^^^^^^^^^^^^^
``length``
~~~~~~~~~~
Specify a number of characters to extract from ``nth``.
If you omit or specify a negative value, this function extracts from ``nth`` to the end.
``options``
~~~~~~~~~~~
.. versionadded:: 11.0.3
Specify the following key.
``default_value``
Specify a string to be returned when a substring is an empty string except when specifying 0 for ``length``.
The default is an empty string.
Return value
------------
``string_substring`` returns a substring extracted under the specified conditions from ``target``.
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