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# 7.3.12. `column_list`

## 7.3.12.1. Summary

`column_list` command lists columns in a table.

## 7.3.12.2. Syntax

This command takes only one required parameter:

    column_list table

## 7.3.12.3. Usage

Here is a simple example of `column_list` command.

Execution example:

    table_create Users TABLE_PAT_KEY ShortText
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_create Users age COLUMN_SCALAR UInt8
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_create Users tags COLUMN_VECTOR ShortText
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_list Users
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         "id",
    #         "UInt32"
    #       ],
    #       [
    #         "name",
    #         "ShortText"
    #       ],
    #       [
    #         "path",
    #         "ShortText"
    #       ],
    #       [
    #         "type",
    #         "ShortText"
    #       ],
    #       [
    #         "flags",
    #         "ShortText"
    #       ],
    #       [
    #         "domain",
    #         "ShortText"
    #       ],
    #       [
    #         "range",
    #         "ShortText"
    #       ],
    #       [
    #         "source",
    #         "ShortText"
    #       ]
    #     ],
    #     [
    #       256,
    #       "_key",
    #       "",
    #       "",
    #       "COLUMN_SCALAR",
    #       "Users",
    #       "ShortText",
    #       []
    #     ],
    #     [
    #       257,
    #       "age",
    #       "/tmp/groonga-databases/commands_column_list.0000101",
    #       "fix",
    #       "COLUMN_SCALAR|PERSISTENT",
    #       "Users",
    #       "UInt8",
    #       []
    #     ],
    #     [
    #       258,
    #       "tags",
    #       "/tmp/groonga-databases/commands_column_list.0000102",
    #       "var",
    #       "COLUMN_VECTOR|PERSISTENT",
    #       "Users",
    #       "ShortText",
    #       []
    #     ]
    #   ]
    # ]

## 7.3.12.4. Parameters

This section describes parameters of `column_list`.

### 7.3.12.4.1. Required parameters

All parameters are required.

#### 7.3.12.4.1.1. `table`

Specifies the name of table to be listed columns.

## 7.3.12.5. Return value

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

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

`HEADER`

> See 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:

> > 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:

> > 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 Pseudo column.

> `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`.

## 7.3.12.6. See also

- column_create

- Column