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.