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# 7.3.12. `column_copy`

## 7.3.12.1. Summary

Added in version 5.0.7.

`column_copy` copies all column values to other column.

You can implement the following features with this command:

> - Changing column configuration

> - Changing table configuration

You can change column configuration by the following steps:

> 1. Create a new column with new configuration

> 2. Copy all values from the current column to the new column

> 3. Remove the current column

> 4. Rename the new column to the current column

You can change table configuration by the following steps:

> 1. Create a new table with new configuration

> 2. Create all same columns to the new table

> 3. Copy all column values from the current table to the new table

> 4. Remove the current table

> 5. Rename the new table to the current table

Concrete examples are showed later.

You can’t copy column values from a `TABLE_NO_KEY` table to another table. And you can’t copy column values to a `TABLE_NO_KEY` table from another table. Because Groonga can’t map records without record key.

You can copy column values from a `TABLE_NO_KEY` table to the same `TABLE_NO_KEY` table.

You can copy column values from a `TABLE_HASH_KEY` / `TABLE_PAT_KEY` / `TABLE_DAT_KEY` table to the same or another `TABLE_HASH_KEY` / `TABLE_PAT_KEY` / `TABLE_DAT_KEY` table.

## 7.3.12.2. Syntax

This command takes four parameters.

All parameters are required:

    column_copy from_table
                from_name
                to_table
                to_name

## 7.3.12.3. Usage

Here are use cases of this command:

> - Changing column configuration

> - Changing table configuration

### 7.3.12.3.1. How to change column configuration

You can change column value type. For example, you can change `UInt32` column value to `ShortText` column value.

You can change column type. For example, you can change `COLUMN_SCALAR` column to `COLUMN_VECTOR` column.

You can move a column to other table. For example, you can move `high_score` column to `Users` table from `Players` table.

Here are basic steps to change column configuration:

> 1. Create a new column with new configuration

> 2. Copy all values from the current column to the new column

> 3. Remove the current column

> 4. Rename the new column to the current column

Here is an example to change column value type to `Int32` from `ShortText`.

Here are schema and data:

Execution example:

    table_create Logs TABLE_HASH_KEY ShortText
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_create Logs serial COLUMN_SCALAR Int32
    # [[0,1337566253.89858,0.000355720520019531],true]
    load --table Logs
    [
    {"_key": "log1", "serial": 1}
    ]
    # [[0,1337566253.89858,0.000355720520019531],1]

The following commands change `Logs.serial` column value type to `ShortText` from `Int32`:

Execution example:

    column_create Logs new_serial COLUMN_SCALAR ShortText
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_copy Logs serial Logs new_serial
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_remove Logs serial
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_rename Logs new_serial serial
    # [[0,1337566253.89858,0.000355720520019531],true]
    select Logs
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         1
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "serial",
    #           "ShortText"
    #         ]
    #       ],
    #       [
    #         1,
    #         "log1",
    #         "1"
    #       ]
    #     ]
    #   ]
    # ]

You can find `Logs.serial` stores `ShortText` value from the response of `select`.

Here is an example to change column type to `COLUMN_VECTOR` from `COLUMN_SCALAR`.

Here are schema and data:

Execution example:

    table_create Entries TABLE_HASH_KEY ShortText
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_create Entries tag COLUMN_SCALAR ShortText
    # [[0,1337566253.89858,0.000355720520019531],true]
    load --table Entries
    [
    {"_key": "entry1", "tag": "Groonga"}
    ]
    # [[0,1337566253.89858,0.000355720520019531],1]

The following commands change `Entries.tag` column to `COLUMN_VECTOR` from `COLUMN_SCALAR`:

Execution example:

    column_create Entries new_tag COLUMN_VECTOR ShortText
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_copy Entries tag Entries new_tag
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_remove Entries tag
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_rename Entries new_tag tag
    # [[0,1337566253.89858,0.000355720520019531],true]
    select Entries
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         1
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "tag",
    #           "ShortText"
    #         ]
    #       ],
    #       [
    #         1,
    #         "entry1",
    #         [
    #           "Groonga"
    #         ]
    #       ]
    #     ]
    #   ]
    # ]

You can find `Entries.tag` stores `COLUMN_VECTOR` value from the response of `select`.

Here is an example to move `high_score` column to `Users` table from `Players` table.

Here are schema and data:

Execution example:

    table_create Players TABLE_HASH_KEY ShortText
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_create Players high_score COLUMN_SCALAR Int32
    # [[0,1337566253.89858,0.000355720520019531],true]
    load --table Players
    [
    {"_key": "player1", "high_score": 100}
    ]
    # [[0,1337566253.89858,0.000355720520019531],1]

The following commands move `high_score` column to `Users` table from `Players` table:

Execution example:

    table_create Users TABLE_HASH_KEY ShortText
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_create Users high_score COLUMN_SCALAR Int32
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_copy Players high_score Users high_score
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_remove Players high_score
    # [[0,1337566253.89858,0.000355720520019531],true]
    select Users
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         1
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "high_score",
    #           "Int32"
    #         ]
    #       ],
    #       [
    #         1,
    #         "player1",
    #         100
    #       ]
    #     ]
    #   ]
    # ]

You can find `Users.high_score` is moved from `Players.high_score` from the response of `select`.

### 7.3.12.3.2. How to change table configuration

You can change table key type. For example, you can change key type to `ShortText` from `Int32`.

You can change table type. For example, you can change `TABLE_HASH_KEY` table to `TABLE_PAT_KEY` table.

You can also change other options such as default tokenizer and normalizer. For example, you can change default tokenizer to `TokenBigramSplitSymbolAlphaDigit` from `TokenBigrm`.

Note

You can’t change `TABLE_NO_KEY` table. Because `TABLE_NO_KEY` doesn’t have record key. Groonga can’t identify copy destination record without record key.

Here are basic steps to change table configuration:

> 1. Create a new table with new configuration

> 2. Create all same columns to the new table

> 3. Copy all column values from the current table to the new table

> 4. Remove the current table

> 5. Rename the new table to the current table

Here is an example to change table key type to `ShortText` from `Int32`.

Here are schema and data:

Execution example:

    table_create IDs TABLE_HASH_KEY Int32
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_create IDs label COLUMN_SCALAR ShortText
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_create IDs used COLUMN_SCALAR Bool
    # [[0,1337566253.89858,0.000355720520019531],true]
    load --table IDs
    [
    {"_key": 100, "label": "ID 100", used: true}
    ]
    # [[0,1337566253.89858,0.000355720520019531],1]

The following commands change `IDs` table key type to `ShortText` from `Int32`:

Execution example:

    table_create NewIDs TABLE_HASH_KEY Int32
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_create NewIDs label COLUMN_SCALAR ShortText
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_create NewIDs used COLUMN_SCALAR Bool
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_copy IDs label NewIDs label
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_copy IDs used  NewIDs used
    # [[0,1337566253.89858,0.000355720520019531],true]
    table_remove IDs
    # [[0,1337566253.89858,0.000355720520019531],true]
    table_rename NewIDs IDs
    # [[0,1337566253.89858,0.000355720520019531],true]
    select IDs
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         1
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "Int32"
    #         ],
    #         [
    #           "label",
    #           "ShortText"
    #         ],
    #         [
    #           "used",
    #           "Bool"
    #         ]
    #       ],
    #       [
    #         1,
    #         100,
    #         "ID 100",
    #         true
    #       ]
    #     ]
    #   ]
    # ]

You can find `IDs` stores `ShortText` key from the response of `select`.

Here is an example to change table type to `TABLE_PAT_KEY` from `TABLE_HASH_KEY`.

Here are schema and data:

Execution example:

    table_create Names TABLE_HASH_KEY ShortText
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_create Names used COLUMN_SCALAR Bool
    # [[0,1337566253.89858,0.000355720520019531],true]
    load --table Names
    [
    {"_key": "alice", "used": false}
    ]
    # [[0,1337566253.89858,0.000355720520019531],1]

The following commands change `Names` table to `TABLE_PAT_KEY` from `TABLE_HASH_KEY`:

Execution example:

    table_create NewNames TABLE_PAT_KEY ShortText
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_create NewNames used COLUMN_SCALAR Bool
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_copy Names used NewNames used
    # [[0,1337566253.89858,0.000355720520019531],true]
    table_remove Names
    # [[0,1337566253.89858,0.000355720520019531],true]
    table_rename NewNames Names
    # [[0,1337566253.89858,0.000355720520019531],true]
    select Names --filter '_key @^ "ali"'
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         1
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "used",
    #           "Bool"
    #         ]
    #       ],
    #       [
    #         1,
    #         "alice",
    #         false
    #       ]
    #     ]
    #   ]
    # ]

You can find `Names` is a `TABLE_PAT_KEY` because `select` can use Prefix search operator. You can’t use Prefix search operator with `TABLE_HASH_KEY`.

## 7.3.12.4. Parameters

This section describes parameters.

### 7.3.12.4.1. Required parameters

All parameters are required.

#### 7.3.12.4.1.1. `from_table`

Specifies the table name of source column.

You can specify any table including `TABLE_NO_KEY` table.

If you specify `TABLE_NO_KEY` table, to_table must be the same table.

Here is an example to use `from_table`.

Here are schema and data:

Execution example:

    table_create FromTable TABLE_HASH_KEY ShortText
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_create FromTable from_column COLUMN_SCALAR ShortText
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_create FromTable to_column   COLUMN_SCALAR ShortText
    # [[0,1337566253.89858,0.000355720520019531],true]
    load --table FromTable
    [
    {"_key": "key1", "from_column": "value1"}
    ]
    # [[0,1337566253.89858,0.000355720520019531],1]
    select FromTable --output_columns _key,from_column,to_column
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         1
    #       ],
    #       [
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "from_column",
    #           "ShortText"
    #         ],
    #         [
    #           "to_column",
    #           "ShortText"
    #         ]
    #       ],
    #       [
    #         "key1",
    #         "value1",
    #         ""
    #       ]
    #     ]
    #   ]
    # ]

You can copy all values to `to_column` from `from_column`:

Execution example:

    column_copy FromTable from_column FromTable to_column
    # [[0,1337566253.89858,0.000355720520019531],true]
    select FromTable --output_columns _key,from_column,to_column
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         1
    #       ],
    #       [
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "from_column",
    #           "ShortText"
    #         ],
    #         [
    #           "to_column",
    #           "ShortText"
    #         ]
    #       ],
    #       [
    #         "key1",
    #         "value1",
    #         "value1"
    #       ]
    #     ]
    #   ]
    # ]

#### 7.3.12.4.1.2. `from_name`

Specifies the column name to be copied values.

See from_table for example.

#### 7.3.12.4.1.3. `to_table`

Specifies the table name of destination column.

You can specify the same table name as from_table when you want to copy column values in the same table.

You can’t specify `TABLE_NO_KEY` table to `to_table` because Groonga can’t identify destination records without record key.

There is one exception. If you specify the same name as `from_table` to `to_table`, you can use `TABLE_NO_KEY` table as `to_table`. Because Groonga can identify destination records when source table and destination table is the same table.

Here is an example to use `to_table`.

Here are schema and data:

Execution example:

    table_create Table TABLE_HASH_KEY ShortText
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_create Table column COLUMN_SCALAR ShortText
    # [[0,1337566253.89858,0.000355720520019531],true]
    table_create ToTable TABLE_HASH_KEY ShortText
    # [[0,1337566253.89858,0.000355720520019531],true]
    column_create ToTable to_column COLUMN_SCALAR ShortText
    # [[0,1337566253.89858,0.000355720520019531],true]
    load --table Table
    [
    {"_key": "key1", "column": "value1"}
    ]
    # [[0,1337566253.89858,0.000355720520019531],1]

You can copy all values to `ToTable.to_column` from `Table.column`:

Execution example:

    column_copy Table column ToTable to_column
    # [[0,1337566253.89858,0.000355720520019531],true]
    select ToTable --output_columns _key,to_column
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         1
    #       ],
    #       [
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "to_column",
    #           "ShortText"
    #         ]
    #       ],
    #       [
    #         "key1",
    #         "value1"
    #       ]
    #     ]
    #   ]
    # ]

#### 7.3.12.4.1.4. `to_name`

Specifies the destination column name.

See to_table for example.

### 7.3.12.4.2. Optional parameters

There is no optional parameter.

## 7.3.12.5. Return value

The command returns `true` as body on success such as:

    [HEADER, true]

If the command fails, error details are in `HEADER`.

See Output format for `HEADER`.