.. -*- rst -*-

.. highlightlang:: none

.. groonga-command
.. database: commands_column_list

``column_list``
===============

Summary
-------

``column_list`` command lists columns in a table.

Syntax
------

``column_list`` command takes one required parameter::

  column_list table

Usage
-----

Here is a simple example of ``column_list`` command.

.. groonga-command
.. include:: ../../example/reference/commands/column_list/column_list.log
.. table_create Users TABLE_PAT_KEY ShortText
.. column_create Users age COLUMN_SCALAR UInt8
.. column_create Users tags COLUMN_VECTOR ShortText
.. column_list Users


Parameters
----------

This section describes parameters of ``column_list``.

Required parameters
^^^^^^^^^^^^^^^^^^^

All parameters are required.

``table``
"""""""""

It specifies the name of table to be listed columns.

Return value
------------

``column_list`` returns the list of column information in the table::

  [
    HEADER,
    [
      COLUMN_LIST_HEADER,
      COLUMN_INFORMATION1,
      COLUMN_INFORMATION2,
      ...
    ]
  ]

``HEADER``

  See :doc:`/reference/command/output_format` about ``HEADER``.

``COLUMN_LIST_HEADER``

  ``COLUMN_LIST_HEADER`` describes about content of each
  ``COLUMN_INFORMATION``.

  ``COLUMN_LIST_HEADER`` is the following format::

    [
      ["id",     "UInt32"],
      ["name",   "ShortText"],
      ["path",   "ShortText"],
      ["type",   "ShortText"],
      ["flags",  "ShortText"],
      ["domain", "ShortText"],
      ["range",  "ShortText"],
      ["source", "ShortText"]
    ]

  It means the following:

    * The first content in ``COLUMN_INFORMATION`` is ``id`` value and
      the value type is ``UInt32``.
    * The second content in ``COLUMN_INFORMATION`` is ``name`` value and
      the value type is ``ShortText``.
    * The third content ....

  See the following ``COLUMN_INFORMATION`` description for details.

  This field provides meta-data of column information. So this field
  will be useful for programs rather than humans.

``COLUMN_INFORMATION``

  Each ``COLUMN_INFORMATION`` is the following format::

    [
      ID,
      NAME,
      PATH,
      TYPE,
      FLAGS,
      DOMAIN,
      RANGE,
      SOURCES
    ]

  ``ID``

    The column ID in the Groonga database. Normally, you don't care
    about it.

  ``NAME``

    The column name.

  ``PATH``

    The path for storing column data.

  ``TYPE``

    The type of the column. It is one of the followings:

    .. list-table::
       :header-rows: 1

       * - Value
         - Description
       * - ``fix``
         - The column is a fixed size column. Scalar column that its
           type is fixed size type is fixed size column.
       * - ``var``
         - The column is a variable size column. Vector column or
           scalar column that its type is variable size type are
           variable size column.
       * - ``index``
         - The column is an index column.

  ``FLAGS``

    The flags of the column. Each flag is separated by ``|`` like
    ``COLUMN_VECTOR|WITH_WEIGHT``. ``FLAGS`` must include one of
    ``COLUMN_SCALAR``, ``COLUMN_VECTOR`` or ``COLUMN_INDEX``. Other
    flags are optional.

    Here is the available flags:

    .. list-table::
       :header-rows: 1

       * - Flag
         - Description
       * - ``COLUMN_SCALAR``
         - The column is a scalar column.
       * - ``COLUMN_VECTOR``
         - The column is a vector column.
       * - ``COLUMN_INDEX``
         - The column is an index column.
       * - ``WITH_WEIGHT``
         - The column can have weight. ``COLUMN_VECTOR`` and ``COLUMN_INDEX``
           may have it. ``COLUMN_SCALAR`` doesn't have it.
       * - ``WITH_SECTION``
         - The column can have section information. ``COLUMN_INDEX``
           may have it.  ``COLUMN_SCALAR`` and ``COLUMN_VECTOR`` don't
           have it.

           Multiple column index has it.
       * - ``WITH_POSITION``
         - The column can have position information. ``COLUMN_INDEX``
           may have it.  ``COLUMN_SCALAR`` and ``COLUMN_VECTOR`` don't
           have it.

           Full text search index must has it.
       * - ``PERSISTENT``
         - The column is a persistent column. It means that the column
           isn't a :doc:`/reference/columns/pseudo`.

  ``DOMAIN``

      The name of table that has the column.

  ``RANGE``

      The value type name of the column. It is a type name or a table
      name.

  ``SOURCES``

      An array of the source column names of the index. If the index
      column is multiple column index, the array has two or more
      source column names.

      It is always an empty array for ``COLUMN_SCALAR`` and
      ``COLUMN_VECTOR``.

See also
--------

* :doc:`/reference/commands/column_create`
* :doc:`/reference/column`
