# Not Null Constraint

The `NOT NULL` constraint specifies a column may not contain NULL values.

## Details

- `INSERT` or `UPDATE` statements containing `NULL` values are rejected. This includes `INSERT` statements that do not include values for any columns that do not have a `DEFAULT` value constraint.

For example, if the table `foo` has columns `a` and `b` (and `b` does not have a `DEFAULT VALUE`), when you run the following command:

      > INSERT INTO foo (a) VALUES (1);

CockroachDB tries to write a `NULL` value into column `b`. If that column has the `NOT NULL` constraint, the `INSERT` statement is rejected.

- You can only define the `NOT NULL` constraint when creating a table; you cannot add it to an existing table. However, you can migrate data from your current table to a new table with the constraint you want to use.

  Note:
  In the future we plan to support adding the `NOT NULL` constraint to existing tables.

- For more information about `NULL`, see Null Handling.

## Syntax

You can only apply the `NOT NULL` constraint to individual columns.

Parameter | Description
--- | ---
`table_name` | The name of the table you're creating.
`column_name` | The name of the constrained column.
`column_type` | The constrained column's data type.
`column_constraints` | Any other column-level constraints you want to apply to this column.
`column_def` | Definitions for any other columns in the table.
`table_constraints` | Any table-level constraints you want to apply.

## Usage example

    > CREATE TABLE IF NOT EXISTS customers (
        customer_id INT         PRIMARY KEY,
        cust_name   STRING(30)  NULL,
        cust_email  STRING(100) NOT NULL
      );

    > INSERT INTO customers (customer_id, cust_name, cust_email) VALUES (1, 'Smith', NULL);

    pq: null value in column "cust_email" violates not-null constraint

    > INSERT INTO customers (customer_id, cust_name) VALUES (1, 'Smith');

    pq: null value in column "cust_email" violates not-null constraint

## See also

- Constraints
- `DROP CONSTRAINT`
- `CHECK` constraint
- `DEFAULT` constraint
- `REFERENCES` constraint (Foreign Key)
- `PRIMARY KEY` constraint
- `UNIQUE` constraint
- `SHOW CONSTRAINTS`