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

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# 8.3.29. `table_create`

## 8.3.29.1. Summary

`table_create` creates a new table in the current database. You need to create one or more tables to store and search data.

## 8.3.29.2. Syntax

`table_create` has many parameters. The required parameter is only `name` and otehrs are optional:

    table_create name
                 [flags=TABLE_HASH_KEY]
                 [key_type=null]
                 [value_type=null]
                 [default_tokenizer=null]
                 [normalizer=null]

## 8.3.29.3. Usage

`table_create` command creates a new persistent table. See Tables for table details.

### 8.3.29.3.1. Create data store table

You can use all table types for data store table. See Tables for all table types.

Table type is specified as `TABLE_${TYPE}` to `flags` parameter.

Here is an example to create `TABLE_NO_KEY` table:

Execution example:

    table_create Logs TABLE_NO_KEY
    # [[0, 1337566253.89858, 0.000355720520019531], true]

The `table_create` command creates a table that is named `Logs` and is `TABLE_NO_KEY` type.

If your records aren't searched by key, `TABLE_NO_KEY` type table is suitable. Because `TABLE_NO_KEY` doesn't support key but it is fast and small table. Storing logs into Groonga database is the case.

If your records are searched by key or referenced by one or more columns, `TABLE_NO_KEY` type isn't suitable. Lexicon for fulltext search is the case.

### 8.3.29.3.2. Create lexicon table

You can use all table types except `TABLE_NO_KEY` for lexicon table. Lexicon table needs key support but `TABLE_NO_KEY` doesn't support key.

Here is an example to create `TABLE_PAT_KEY` table:

Execution example:

    table_create Lexicon TABLE_PAT_KEY ShortText --default_tokenizer TokenBigram --normalizer NormalizerAuto
    # [[0, 1337566253.89858, 0.000355720520019531], true]

The `table_create` command creates the following table:

- The table is named `Lexicon`.
- The table is `TABLE_PAT_KEY` type table.
- The table's key is `ShortText` type.
- The table uses `TokenBigram` tokenizer to extract tokens from a normalized text.
- The table uses `NormalizerAuto` normalizer to normalize a text.

`TABLE_PAT_KEY` is suitable table type for lexicon table. Lexicon table is used for fulltext search.

In fulltext search, predictive search may be used for fuzzy search. Predictive search is supported by `TABLE_PAT_KEY` and `TABLE_DAT_KEY`.

Lexicon table has many keys because a fulltext target text has many tokens. Table that has many keys should consider table size because large table requires large memory. Requiring large memory causes disk I/O. It blocks fast search. So table size is important for a table that has many keys. `TABLE_PAT_KEY` is less table size than `TABLE_DAT_KEY`.

Because of the above reasons, `TABLE_PAT_KEY` is suitable table type for lexicon table.

### 8.3.29.3.3. Create tag index table

You can use all table types except `TABLE_NO_KEY` for tag index table. Tag index table needs key support but `TABLE_NO_KEY` doesn't support key.

Here is an example to create `TABLE_HASH_KEY` table:

Execution example:

    table_create Ages TABLE_DAT_KEY UInt32
    # [[0, 1337566253.89858, 0.000355720520019531], true]

The `table_create` command creates a table that is named `Tags`, is `TABLE_HASH_KEY` type and has `ShortText` type key.

`TABLE_HASH_KEY` or `TABLE_DAT_KEY` are suitable table types for tag index table.

If you need only exact match tag search feature, `TABLE_HASH_KEY` is suitable. It is the common case.

If you also need predictive tag search feature (for example, searching `"groonga"` by `"gr"` keyword.), `TABLE_DAT_KEY` is suitable. `TABLE_DAT_KEY` is large table size but it is not important because the number of tags will not be large.

### 8.3.29.3.4. Create range index table

You can use `TABLE_PAT_KEY` and `TABLE_DAT_KEY` table types for range index table. Range index table needs range search support but `TABLE_NO_KEY` and `TABLE_HASH_KEY` don't support it.

Here is an example to create `TABLE_DAT_KEY` table:

Execution example:

    table_create Ages TABLE_DAT_KEY UInt32
    # [[0, 1337566253.89858, 0.000355720520019531], true]

The `table_create` command creates a table that is named `Ages`, is `TABLE_DAT_KEY` type and has `UInt32` type key.

`TABLE_PAT_KEY` and `TABLE_DAT_KEY` are suitable table types for range index table.

If you don't have many indexed items, `TABLE_DAT_KEY` is suitable. Index for age is the case in the above example. Index for age will have only 0-100 items because human doesn't live so long.

If you have many indexed items, `TABLE_PAT_KEY` is suitable. Because `TABLE_PAT_KEY` is smaller than `TABLE_DAT_KEY`.

## 8.3.29.4. Parameters

This section describes all parameters.

### 8.3.29.4.1. `name`

It specifies a table name to be created. `name` must be specified.

Here are available characters:

- `0` .. `9` (digit)
- `a` .. `z` (alphabet, lower case)
- `A` .. `Z` (alphabet, upper case)
- `#` (hash)
- `@` (at mark)
- `-` (hyphen)
- `_` (underscore) (NOTE: Underscore can't be used as the first character.)

You need to create a name with one or more the above chracters. Note that you cannot use `_` as the first character such as `_name`.

### 8.3.29.4.2. `flags`

It specifies a table type and table customize options.

Here are available flags:

flags | description
`TABLE_NO_KEY` | Array table.
`TABLE_HASH_KEY` | Hash table.
`TABLE_PAT_KEY` | Patricia trie.
`TABLE_DAT_KEY` | Double Array trie.
`KEY_WITH_SIS` | Enable Semi Infinite String. Require `TABLE_PAT_KEY`.

Note

Since Groonga 2.1.0 `KEY_NORMALIZE` flag is deprecated. Use `normalizer` option with `NormalizerAuto` instead.

You must specify one of `TABLE_${TYPE}` flags. You cannot specify two or more `TABLE_${TYPE}` flags. For example, `TABLE_NO_KEY|TABLE_HASH_KEY` is invalid.

You can combine flags with `|` (vertical bar) such as `TABLE_PAT_KEY|KEY_WITH_SIS`.

See Tables for difference between table types.

The default flags are `TABLE_HASH_KEY`.

### 8.3.29.4.3. `key_type`

It specifies key type.

If you specify `TABLE_HASH_KEY`, `TABLE_PAT_KEY` or `TABLE_DAT_KEY` as `flags` parameter, you need to specify `key_type` option.

See データ型 for all types.

The default value is none.

### 8.3.29.4.4. `value_type`

It specifies value type.

You can use value when you specify `TABLE_NO_KEY`, `TABLE_HASH_KEY` or `TABLE_PAT_KEY` as `flags` parameter. Value type must be a fixed size type. For example, `UInt32` can be used but `ShortText` cannot be used. Use columns instead of value.

The default value is none.

### 8.3.29.4.5. `default_tokenizer`

It specifies the default tokenizer that is used on searching and data loading.

You cannot use `default_tokenizer` with `TABLE_NO_KEY` because `TABLE_NO_KEY` cannot be used for index.

You must specify `default_tokenizer` for a table that is used for fulltext search index.

See Tokenizers for all tokenizers

The default value is none.

### 8.3.29.4.6. `normalizer`

It specifies a normalizer that is used to normalize key.

You cannot use `normalizer` with `TABLE_NO_KEY` because `TABLE_NO_KEY` doesn't support key.

See Normalizers for all normalizsers.

The default value is none.

## 8.3.29.5. Return value

`table_create` returns `true` as body on success such as:

    [HEADER, true]

If `table_create` fails, error details are in `HEADER`.

See Output format for `HEADER`.

## 8.3.29.6. See also

- Tables
- column_create
- Tokenizers
- Normalizers
- Output format

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