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---
> **Documentation Index:** Fetch the complete configuration index at https://ydb.tech/docs/en/llms.txt

# Changing the `NOT NULL` constraint

The `NOT NULL` constraint is a column-level data integrity constraint that prohibits writing `NULL` values. It ensures that the column always contains a valid value.


## Dropping `NOT NULL`

`DROP NOT NULL` removes the `NOT NULL` constraint from the specified column.

For example, the following query will remove the `NOT NULL` constraint from column `column_name` in table `table_name`:


```yql
ALTER TABLE table_name ALTER COLUMN column_name DROP NOT NULL;
```


`DROP NOT NULL` can be applied to non-key columns in both row-oriented and column-oriented tables.

## See also

* [ALTER COLUMN](https://ydb.tech/docs/en/yql/reference/syntax/alter_table/columns.md)