> ## Documentation Index
> Fetch the complete documentation index at: https://cockroachlabs.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.
# NOT NULL constraint
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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:
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> 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.
* To add the `NOT NULL` constraint to an existing table column, use the `ALTER COLUMN` statement.
* 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
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> CREATE TABLE IF NOT EXISTS customers (
customer_id INT PRIMARY KEY,
cust_name STRING(30) NULL,
cust_email STRING(100) NOT NULL
);
```
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> INSERT INTO customers (customer_id, cust_name, cust_email) VALUES (1, 'Smith', NULL);
```
```text theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
pq: null value in column "cust_email" violates not-null constraint
```
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> INSERT INTO customers (customer_id, cust_name) VALUES (1, 'Smith');
```
```text theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
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`
* `NULL HANDLING`