docs/content/flink/default-value.md

---
title: "Default Value"
weight: 8
type: docs
aliases:
- /flink/default-value.html
---
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# 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

Flink SQL does not have native support for default values, so we can only create a table without default values:

```sql
CREATE TABLE my_table (
    a BIGINT,
    b STRING,
    c INT,
    tags ARRAY<STRING>,
    properties MAP<STRING, STRING>,
    nested ROW<x INT, y STRING>
);
```

We support the procedure of modifying column default values in Flink. You can add default value definitions after
creating the table:

```sql
-- Set simple type default values
CALL sys.alter_column_default_value('default.my_table', 'b', 'my_value');
CALL sys.alter_column_default_value('default.my_table', 'c', '5');

-- Set complex type default values
CALL sys.alter_column_default_value('default.my_table', 'tags', '[tag1, tag2, tag3]');
CALL sys.alter_column_default_value('default.my_table', 'properties', '{key1 -> value1, key2 -> value2}');
CALL sys.alter_column_default_value('default.my_table', 'nested', '{42, default_value}');
```

## Insert Table

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

For example:

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

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