> ## 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.
# Default Value Constraint
export const InternalLink = ({version, path = "", children, ...props}) => {
let detectedVersion = version || "stable";
if (typeof window !== 'undefined' && !version) {
const match = window.location.pathname.match(/\/docs\/([^/]+)/);
if (match) {
detectedVersion = match[1];
}
}
const normalizedPath = path.startsWith("/") ? path.slice(1) : path;
return
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;
};
The `DEFAULT` value constraint specifies a value to write into the constrained column if one is not defined in an `INSERT` statement. The value may be either a hard-coded literal or an expression that is evaluated at the time the row is created.
## Details
* The data type of the `DEFAULT` value must be the same as the data type of the column.
* The `DEFAULT` value constraint only applies if the column does not have a value specified in the `INSERT` statement. You can still insert a `NULL` into an optional (nullable) column by explicitly inserting `NULL`. For example, `INSERT INTO foo VALUES (1, NULL);`.
## Syntax
You can only apply the `DEFAULT` value constraint to individual columns.
You can also add the `DEFAULT` value constraint to an existing table through `ALTER COLUMN`.
| 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. |
| `default_value` | The value you want to insert by default, which must evaluate to the same data type as the `column_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. |
## Example
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> CREATE TABLE inventories (
product_id INT,
warehouse_id INT,
quantity_on_hand INT DEFAULT 100,
PRIMARY KEY (product_id, warehouse_id)
);
```
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> INSERT INTO inventories (product_id, warehouse_id) VALUES (1,20);
```
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> INSERT INTO inventories (product_id, warehouse_id, quantity_on_hand) VALUES (2,30, NULL);
```
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> SELECT * FROM inventories;
```
```
+------------+--------------+------------------+
| product_id | warehouse_id | quantity_on_hand |
+------------+--------------+------------------+
| 1 | 20 | 100 |
| 2 | 30 | NULL |
+------------+--------------+------------------+
```
If the `DEFAULT` value constraint is not specified and an explicit value is not given, a value of `NULL` is assigned to the column.
## See also
* Constraints
* `ALTER COLUMN`
* `CHECK` constraint
* `REFERENCES` constraint (Foreign Key)
* `NOT NULL` constraint
* `PRIMARY KEY` constraint
* `UNIQUE` constraint
* `SHOW CONSTRAINTS`