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CREATE TABLE

Creating tables is one of the most complicated operations for many databases because you might need to:

  • Manually specify the engine
  • Manually specify the indexes
  • And even specify the data partitions or data shard

Databend aims to be easy to use by design and does NOT require any of those operations when you create a table. Moreover, the CREATE TABLE statement provides these options to make it much easier for you to create tables in various scenarios:

CREATE TABLE​

CREATE [TRANSIENT] TABLE [IF NOT EXISTS] [db.]table_name
(
    <column_name> <data_type> [ NOT NULL | NULL] [ { DEFAULT <constant_expr> }],
    <column_name> <data_type> [ NOT NULL | NULL] [ { DEFAULT <constant_expr> }],
    ...
) [CLUSTER BY(<expr> [, <expr>, ...] )]

<data_type>:
  TINYINT
| SMALLINT 
| INT
| BIGINT
| FLOAT
| DOUBLE
| DATE
| TIMESTAMP 
| VARCHAR
| ARRAY
| VARIANT
tip

Data type reference:

For detailed information about the CLUSTER BY clause, see SET CLUSTER KEY.

CREATE TABLE ... LIKE​

Creates a table with the same column definitions as an existing table. Column names, data types, and their non-NUll constraints of the existing will be copied to the new table.

Syntax:

CREATE TABLE [IF NOT EXISTS] [db.]table_name
LIKE [db.]origin_table_name

This command does not include any data or attributes (such as CLUSTER BY, TRANSIENT, and COMPRESSION) from the original table, and instead creates a new table using the default system settings.

WORKAROUND
  • CLUSTER BY can be added back using ALTER TABLE. See ALTER CLUSTER KEY for details.
  • TRANSIENT and COMPRESSION can be explicitly specified when you create a new table with this command. For example,
create transient table t_new like t_old;

create table t_new compression='lz4' like t_old;

CREATE TABLE ... AS​

Creates a table and fills it with data computed by a SELECT command.

Syntax:

CREATE TABLE [IF NOT EXISTS] [db.]table_name
AS SELECT query

This command does not include any attributes (such as CLUSTER BY, TRANSIENT, and COMPRESSION) from the original table, and instead creates a new table using the default system settings.

WORKAROUND
  • CLUSTER BY can be added back using ALTER TABLE. See ALTER CLUSTER KEY for details.
  • TRANSIENT and COMPRESSION can be explicitly specified when you create a new table with this command. For example,
create transient table t_new as select * from t_old;

create table t_new compression='lz4' as select * from t_old;

CREATE TRANSIENT TABLE​

Creates a transient table.

Transient tables are used to hold transitory data that does not require a data protection or recovery mechanism. Dataebend does not hold historical data for a transient table so you will not be able to query from a previous version of the transient table with the Time Travel feature, for example, the AT clause in the SELECT statement will not work for transient tables. Please note that you can still drop and undrop a transient table.

Transient tables help save your storage expenses because they do not need extra space for historical data compared to non-transient tables. See example for detailed explanations.

Syntax:

CREATE TRANSIENT TABLE ...

CREATE TABLE ... SNAPSHOT_LOCATION​

Creates a table and inserts data from a snapshot file.

Databend automatically creates snapshots when data updates occur, so a snapshot can be considered as a view of your data at a time point in the past. Databend may store many snapshots of a table (depending on the number of update operations you performed) for the Time Travel feature that allows you to query, back up, and restore from a previous version of your data within the retention period (24 hours by default).

This command enables you to insert the data stored in a snapshot file when you create a table. Please note that the table you create must have same column definitions as the data from the snapshot.

Syntax:

CREATE TABLE [IF NOT EXISTS] [db.]table_name
(
    <column_name> <data_type> [ NOT NULL | NULL] [ { DEFAULT <expr> }],
    <column_name> <data_type> [ NOT NULL | NULL] [ { DEFAULT <expr> }],
    ...
)
SNAPSHOT_LOCATION = '<SNAPSHOT_FILENAME>';

To obtain the snapshot information (including the snapshot locations) of a table, execute the following command:

SELECT * 
FROM   Fuse_snapshot('<database_name>', '<table_name>');

CREATE TABLE ... EXTERNAL_LOCATION​

Creates a table and specifies an S3 bucket for the data storage instead of the FUSE engine.

Databend stores the table data in the location configured in the file databend-query.toml by default. This option enables you to store the data (in parquet format) in a table in another bucket instead of the default one.

Syntax:

CREATE TABLE [IF NOT EXISTS] [db.]table_name

    <column_name> <data_type> [ NOT NULL | NULL] [ { DEFAULT <expr> }],
    <column_name> <data_type> [ NOT NULL | NULL] [ { DEFAULT <expr> }],
    ...

's3://<bucket>/[<path>]' 
CONNECTION = (
        ENDPOINT_URL = 'https://<endpoint-URL>'
        ACCESS_KEY_ID = '<your-access-key-ID>'
        SECRET_ACCESS_KEY = '<your-secret-access-key>'
        REGION = '<region-name>'
        ENABLE_VIRTUAL_HOST_STYLE = 'true'|'false'
  );
ParameterDescriptionRequired
s3://<bucket>/[<path>]Files are in the specified external location (S3-like bucket)YES
ENDPOINT_URLThe bucket endpoint URL starting with "https://". To use a URL starting with "http://", set allow_insecure to true in the [storage] block of the file databend-query-node.toml.Optional
ACCESS_KEY_IDYour access key ID for connecting the AWS S3 compatible object storage. If not provided, Databend will access the bucket anonymously.Optional
SECRET_ACCESS_KEYYour secret access key for connecting the AWS S3 compatible object storage.Optional
REGIONAWS region name. For example, us-east-1.Optional
ENABLE_VIRTUAL_HOST_STYLEIf you use virtual hosting to address the bucket, set it to "true".Optional

Column Nullable​

By default, all columns are not nullable(NOT NULL), if you want to specify a column default to NULL, please use:

CREATE TABLE [IF NOT EXISTS] [db.]table_name
(
    <column_name> <data_type> NULL,
     ...
)

Let check it out how difference the column is NULL or NOT NULL.

Create a table t_not_null which column with NOT NULL(Databend Column is NOT NULL by default):

CREATE TABLE t_not_null(a INT);
DESC t_not_null;
+-------+-------+------+---------+
| Field | Type  | Null | Default |
+-------+-------+------+---------+
| a     | Int32 | NO   | 0       |
+-------+-------+------+---------+

Create another table t_null column with NULL:

CREATE TABLE t_null(a INT NULL);
DESC t_null;
+-------+-------+------+---------+
| Field | Type  | Null | Default |
+-------+-------+------+---------+
| a     | Int32 | YES  | NULL    |
+-------+-------+------+---------+

Default Values​

DEFAULT <constant_expression>

Specify a default value(constant expression) inserted in the column if a value is not specified via an INSERT or CREATE TABLE AS SELECT statement.

For example:

CREATE TABLE t_default_value(a TINYINT UNSIGNED, b VARCHAR DEFAULT 'b');

Desc the t_default_value table:

DESC t_default_value;
+-------+------------------+------+---------+-------+
| Field | Type             | Null | Default | Extra |
+-------+------------------+------+---------+-------+
| a     | TINYINT UNSIGNED | NO   | 0       |       |
| b     | VARCHAR          | NO   | b       |       |
+-------+------------------+------+---------+-------+

Insert a value:

INSERT INTO T_default_value(a) VALUES(1);

Check the table values:

SELECT * FROM t_default_value;
+------+------+
| a    | b    |
+------+------+
|    1 | b    |
+------+------+

MySQL Compatibility​

Databend’s syntax is difference from MySQL mainly in the data type and some specific index hints.

Examples​

Create Table​

Create a table with a default value for a column (in this case, the genre column has 'General' as the default value):

CREATE TABLE books (
    id BIGINT UNSIGNED,
    title VARCHAR,
    genre VARCHAR DEFAULT 'General'
);

Describe the table to confirm the structure and the default value for the genre column:

DESC books;
+-------+-----------------+------+---------+-------+
| Field | Type            | Null | Default | Extra |
+-------+-----------------+------+---------+-------+
| id    | BIGINT UNSIGNED | NO   | 0       |       |
| title | VARCHAR         | NO   | ""      |       |
| genre | VARCHAR         | NO   | 'General'|       |
+-------+-----------------+------+---------+-------+

Insert a row without specifying the genre:

INSERT INTO books(id, title) VALUES(1, 'Invisible Stars');

Query the table and notice that the default value 'General' has been set for the genre column:

SELECT * FROM books;
+----+----------------+---------+
| id | title          | genre   |
+----+----------------+---------+
|  1 | Invisible Stars| General |
+----+----------------+---------+

Create Table ... Like​

Create a new table (books_copy) with the same structure as an existing table (books):

CREATE TABLE books_copy LIKE books;

Check the structure of the new table:

DESC books_copy;
+-------+-----------------+------+---------+-------+
| Field | Type            | Null | Default | Extra |
+-------+-----------------+------+---------+-------+
| id    | BIGINT UNSIGNED | NO   | 0       |       |
| title | VARCHAR         | NO   | ""      |       |
| genre | VARCHAR         | NO   | 'General'|       |
+-------+-----------------+------+---------+-------+

Insert a row into the new table and notice that the default value for the genre column has been copied:

INSERT INTO books_copy(id, title) VALUES(1, 'Invisible Stars');

SELECT * FROM books_copy;
+----+----------------+---------+
| id | title          | genre   |
+----+----------------+---------+
|  1 | Invisible Stars| General |
+----+----------------+---------+

Create Table ... As​

Create a new table (books_backup) that includes data from an existing table (books):

CREATE TABLE books_backup AS SELECT * FROM books;

Describe the new table and notice that the default value for the genre column has NOT been copied:

DESC books_backup;
+-------+-----------------+------+---------+-------+
| Field | Type            | Null | Default | Extra |
+-------+-----------------+------+---------+-------+
| id    | BIGINT UNSIGNED | NO   | 0       |       |
| title | VARCHAR         | NO   | ""      |       |
| genre | VARCHAR         | NO   | NULL    |       |
+-------+-----------------+------+---------+-------+

Query the new table and notice that the data from the original table has been copied:

SELECT * FROM books_backup;
+----+----------------+---------+
| id | title          | genre   |
+----+----------------+---------+
|  1 | Invisible Stars| General |
+----+----------------+---------+

Create Transient Table​

Create a transient table (temporary table) that automatically deletes data after a specified period of time:

-- Create a transient table
CREATE TRANSIENT TABLE visits (
  visitor_id BIGINT
);

-- Insert values
INSERT INTO visits VALUES(1);
INSERT INTO visits VALUES(2);
INSERT INTO visits VALUES(3);

-- Check the inserted data
SELECT * FROM visits;
+-----------+
| visitor_id |
+-----------+
|         1 |
|         2 |
|         3 |
+-----------+

Create Table ... Snapshot_Location​

Create a table from a specific snapshot, allowing you to create a new table based on the data at a specific point in time:

```sql
CREATE TABLE members 
  ( 
     name VARCHAR 
  ); 

INSERT INTO members 
VALUES     ('Amy'); 

SELECT snapshot_id, 
       timestamp, 
       snapshot_location 
FROM   fuse_snapshot('default', 'members'); 
+-----------------------------------+----------------------------+------------------------------------------------------------+
| snapshot_id                       | timestamp                  | snapshot_location                                          |
+-----------------------------------+----------------------------+------------------------------------------------------------+
|  b5931727ee404869ab99b25bf9e672a9 | 2022-08-29 17:53:54.243561 | 418920/604411/_ss/b5931727ee404869ab99b25bf9e672a9_v1.json |
+-----------------------------------+----------------------------+------------------------------------------------------------+

INSERT INTO members 
VALUES     ('Bob'); 

SELECT snapshot_id, 
       timestamp, 
       snapshot_location 
FROM   fuse_snapshot('default', 'members'); 
+----------------------------------+----------------------------+------------------------------------------------------------+
| snapshot_id                      | timestamp                  | snapshot_location                                          |
|----------------------------------|----------------------------|------------------------------------------------------------|
| b5931727ee404869ab99b25bf9e672a9 | 2022-08-29 17:53:54.243561 | 418920/604411/_ss/b5931727ee404869ab99b25bf9e672a9_v1.json |
| 12637e70dd1c4abbab15470fa0a6d69b | 2022-08-29 18:04:18.973272 | 418920/604411/_ss/12637e70dd1c4abbab15470fa0a6d69b_v1.json |
+----------------------------------+----------------------------+------------------------------------------------------------+

-- Create a new table with a snapshot (ID: b5931727ee404869ab99b25bf9e672a9)
CREATE TABLE members_previous 
  ( 
     name VARCHAR 
  )
snapshot_location='418920/604411/_ss/b5931727ee404869ab99b25bf9e672a9_v1.json';

-- The created table contains "Amy" that is stored in the snapshot
SELECT * 
FROM   members_previous; 
---
Amy

Create Table ... External_Location​

Create a table with data stored on an external location, such as Amazon S3:

-- Create a table named `mytable` and specify the location `s3://testbucket/admin/data/` for the data storage
CREATE TABLE mytable (
  a INT
) 
external_location='s3://testbucket/admin/data/' 
connection=(
  ACCESS_KEY_ID='<your_aws_key_id>' 
  SECRET_ACCESS_KEY='<your_aws_secret_key>' 
  endpoint_url='https://s3.amazonaws.com'
);