DDL

Used to define the structure and organization of the database.

CREATE DATABASE

CREATE DATABASE [IF NOT EXISTS] db_name [WITH db_options];

db_options:
    db_option ...

db_option: {
      TTL value
    | SHARD value
    | VNODE_DURATION value
    | REPLICA value
    | PRECISION {'ms' | 'us' | 'ns'}
}

Options	Description
TTL	Data expiration time, default unlimited storage, supported units: d, h, m.Example: TTL 10d, TTL 180m.
SHARD	Indicates the number of shards, default: 1.
VNODE_DURATION	The time window length of the data in SHARD, default 365 days, supported units: d, h, m.Example: TTL 10d, TTL 180m.
REPLICA	The number of replicas of the data in the cluster, default is 1.(Note: The number of copies must be less than or equal to the data nodes of tskv in the cluster).
PRECISION	The timestamp precision of the database, default is ns.Supported units: ms, us, ns

View the CREATE DATABASE example

Create a database, and retain the policy as unlimited length.

CREATE DATABASE oceanic_station;

Create a database, set the expiration time to 180 days, and each time window to 7 days.

For data expiration policy, please refer to Sharding Rules

CREATE DATABASE oceanic_station WITH TTL '180d' SHARD 1 VNODE_DURATION '7d';

Set the Vnode replication factor quantity.

CREATE DATABASE oceanic_station WITH SHARD 2;

Set the timestamp precision.

The time precision can only be specified when creating the database and cannot be changed afterwards.

CREATE DATABASE oceanic_station WITH PRECISION 'ms';

CREATE TABLE

CREATE TABLE uses CnosDB TSKV to store data, supporting storage of some SQL data types as follows:

• BIGINT

• BIGINT UNSIGNED

• BOOLEAN

• TIMESTAMP

• STRING

• DOUBLE

In addition, the structure of the CnosDB table needs to follow certain specifications, please refer to Basic Concepts.

CREATE TABLE [IF NOT EXISTS] tb_name
(field_definition [, field_definition ] ... [, TAGS(tg_name [, tg_name] ...)]);

field_definition:
    column_name data_type [field_codec_type]
    
field_codec_type:
    CODEC(code_type)

View the CREATE TABLE example

Create a table.

The time field can be omitted when creating a table.

CREATE TABLE air(
    visibility DOUBLE,
    temperature DOUBLE,
    pressure DOUBLE,
    TAGS(station)
);

Create a table and specify the compression algorithm.

Specify the compression algorithm of visibility as QUANTILE, do not compress temperature, and use the default compression algorithm for pressure.

Different data types can specify different compression algorithms, for supported list please refer to Compression Algorithm.

CREATE TABLE air(
    visibility DOUBLE CODEC(QUANTILE),
    temperature DOUBLE CODEC(NULL),
    pressure DOUBLE,
    TAGS(station)
);

If you need to perform other operations on the table created, please refer to INSERT, ALTER TABLE, DROP TABLE.

CREATE EXTERNAL TABLE

The external table is read-only and cannot perform DML operations.

-- Column definitions can not be specified for PARQUET files

CREATE EXTERNAL TABLE [ IF NOT EXISTS ] tb_name 
    ( field_definition [, field_definition] ... ) tb_option;

field_definition:
    column_name data_type [ NULL ]

tb_option: {
      STORED AS { PARQUET | NDJSON | CSV | AVRO }
    | [ WITH HEADER ROW ]
    | [ DELIMITER 'a_single_char' ]
    | [ PARTITIONED BY ( column_name, [, ... ] ) ]
    | LOCATION '<file>'
}

Options	Description
STORED AS	Specify the format of the file, supporting PARQUET, NDJSON, CSV, AVRO.
WITH HEADER ROW	Only effective when STORED AS CSV, used to specify the Header in the CSV file.
DELIMITER	Only effective when STORED AS CSV, used to specify the delimiter in the CSV file.
PARTITIONED BY	Partitioning by the columns specified when creating the table.
LOCATION	Location of the associated file, supports directories.

View the CREATE EXTERNAL TABLE example

Create an external table and specify a local CSV file.

External tables can use all data types (excluding INTERVAL and some other special types) and are not constrained by the CnosDB native model.

CREATE EXTERNAL TABLE cpu (
     cpu_hz  DECIMAL(10,6) NOT NULL,
     temp  DOUBLE NOT NULL,
     version_num  BIGINT NOT NULL,
     is_old  BOOLEAN NOT NULL,
     weight  DECIMAL(12,7) NOT NULL
)
STORED AS CSV
WITH HEADER ROW
LOCATION 'tests/data/csv/cpu.csv';

CREATE STREAM TABLE

tip

Need a source table, STREAM table does not support ALTER

CREATE STREAM TABLE [IF NOT EXISTS] table_name(field_definition [, field_definition] ...)
    WITH (db = 'db_name', table = 'table_name', event_time_column = 'time_column')
    engine = tskv;

field_definition: 
    column_name data_type

Syntax:DROP TABLE

ALTER DATABASE

ALTER DATABASE can modify all parameters set in the database (excluding PRECISION), you can query the current database parameter settings using the DESCRIBE DATABASE command.

ALTER DATABASE db_name [alter_db_options]

alter_db_options:
    SET db_option

db_option: {
      TTL value
    | SHARD value
    | VNODE_DURATION value
    | REPLICA value
}

View the ALTER DATABASE example

Modify TTL.

ALTER DATABASE oceanic_station SET TTL '30d';

**Modify VNODE_DURATION **.

Modifying VNODE_DURATION will not affect existing Vnodes.

ALTER DATABASE oceanic_station SET VNODE_DURATION '7d';

ALTER TABLE

tip

Support modifying/deleting columns of FIELD types, column types can be queried using the DESCRIBE TABLE syntax.

Do not support modifying the column name time.

ALTER TABLE tb_name alter_table_option;

alter_table_option: {
      ADD FIELD col_name [data_type] [CODEC(code_type)]
    | ALTER col_name SET CODEC(code_type)
    | DROP col_name
    | RENAME COLUMN col_name TO new_col_name
}

View the ALTER TABLE example

Add a column of type FIELD and specify the compression algorithm.

ALTER TABLE air ADD FIELD humidity DOUBLE CODEC(DEFAULT);

Modify the compression algorithm of humidity to QUANTILE.

ALTER TABLE air ALTER humidity SET CODEC(QUANTILE);

Delete humidity.

ALTER TABLE air DROP humidity;

DROP DATABASE

DROP DATABASE [IF EXISTS] db_name;

View the DROP DATABASE example

Delete the database, and the database will be immediately deleted.

DROP DATABASE oceanic_station;

DROP TABLE

DROP TABLE [ IF EXISTS ] tb_name;

View the DROP TABLE example

DROP TABLE air;