Default Value

Paimon allows specifying default values for columns. When users write to these tables without explicitly providing values for certain columns, Paimon automatically generates default values for these columns.

Create Table

You can create a table with columns with default values using the following SQL:

CREATE TABLE my_table (
    a BIGINT,
    b STRING DEFAULT 'my_value',
    c INT DEFAULT 5,
    tags ARRAY<STRING> DEFAULT ARRAY('tag1', 'tag2', 'tag3'),
    properties MAP<STRING, STRING> DEFAULT MAP('key1', 'value1', 'key2', 'value2'),
    nested STRUCT<x: INT, y: STRING> DEFAULT STRUCT(42, 'default_value')
);

Insert Table

For SQL commands that execute table writes, such as the INSERT, UPDATE, and MERGE commands, the DEFAULT keyword or NULL value is parsed into the default value specified for the corresponding column.

For example:

INSERT INTO my_table (a) VALUES (1), (2);

SELECT * FROM my_table;
-- result: [[1, my_value, 5, [tag1, tag2, tag3], {'key1' -> 'value1', 'key2' -> 'value2'}, {42, default_value}],
--          [2, my_value, 5, [tag1, tag2, tag3], {'key1' -> 'value1', 'key2' -> 'value2'}, {42, default_value}]]

Alter Default Value

Paimon supports alter column default value.

For example:

CREATE TABLE T (a INT, b INT DEFAULT 2);

INSERT INTO T (a) VALUES (1);
-- result: [[1, 2]]

ALTER TABLE T ALTER COLUMN b SET DEFAULT 3;

INSERT INTO T (a) VALUES (2);
-- result: [[1, 2], [2, 3]]

The default value of 'b' column has been changed to 3 from 2. You can also alter default values for complex types:

ALTER TABLE my_table ALTER COLUMN tags SET DEFAULT ARRAY('new_tag1', 'new_tag2');

INSERT INTO my_table (a) VALUES (3);
-- result: [[1, my_value, 5, [tag1, tag2, tag3], {'key1' -> 'value1', 'key2' -> 'value2'}, {42, default_value}],
--          [2, my_value, 5, [tag1, tag2, tag3], {'key1' -> 'value1', 'key2' -> 'value2'}, {42, default_value}],
--          [3, my_value, 5, [new_tag1, new_tag2], {'key1' -> 'value1', 'key2' -> 'value2'}, {42, default_value}]]

ALTER TABLE my_table ALTER COLUMN properties SET DEFAULT MAP('new_key', 'new_value');

INSERT INTO my_table (a) VALUES (4);
-- result: [[1, my_value, 5, [tag1, tag2, tag3], {'key1' -> 'value1', 'key2' -> 'value2'}, {42, default_value}],
--          [2, my_value, 5, [tag1, tag2, tag3], {'key1' -> 'value1', 'key2' -> 'value2'}, {42, default_value}],
--          [3, my_value, 5, [new_tag1, new_tag2], {'key1' -> 'value1', 'key2' -> 'value2'}, {42, default_value}],
--          [4, my_value, 5, [new_tag1, new_tag2], {'new_key' -> 'new_value'}, {42, default_value}]]

Limitation

Not support alter table add column with default value, for example: ALTER TABLE T ADD COLUMN d INT DEFAULT 5;.