> ## Documentation Index
> Fetch the complete documentation index at: https://www.cockroachlabs.com/llms.txt
> Use this file to discover all available pages before exploring further.
# CREATE DOMAIN
export const InternalLink = ({version, path = "", children, ...props}) => {
let detectedVersion = version || "stable";
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const match = window.location.pathname.match(/\/docs\/([^/]+)/);
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detectedVersion = match[1];
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}
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return
{children}
;
};
The `CREATE DOMAIN` statement creates a new domain data type in a database. A domain is based on an existing data type, with optional constraints that restrict its allowed values and an optional `DEFAULT` value. After the domain is created, it can only be referenced from the database that contains the domain.
The `CREATE DOMAIN` statement performs a schema change. For more information about how online schema changes work in CockroachDB, refer to Online Schema Changes.
## Synopsis
## Parameters
| Parameter | Description |
| ----------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `type_name` | The name of the domain. You can qualify the name with a database and schema name (for example, `db.domainname`), but after the domain is created, it can only be referenced from the database that contains the domain. |
| `typename` | The base data type of the domain. |
| `DEFAULT a_expr` | The default value for columns that use the domain data type. A column inherits this value unless the column defines its own `DEFAULT` value. |
| `NOT NULL` | Disallow `NULL` values for the domain. |
| `NULL` | Allow `NULL` values for the domain. This is the default behavior; the clause is accepted for PostgreSQL compatibility. |
| `CONSTRAINT name` | The name of a `CHECK` constraint. If not specified, CockroachDB generates a name (for example, `order_qty_check` for a domain named `order_qty`). |
| `CHECK (a_expr)` | A `CHECK` expression that values of the domain must satisfy. Use the `VALUE` keyword to reference the value being tested. A domain can have multiple `CHECK` constraints. |
## Required privileges
To create a domain, the user must have the `CREATE` privilege on the parent database and the schema in which the domain is being created.
To use a domain in a table (for example, when defining a column's type), the user must have the `USAGE` privilege on the domain.
## Details
* Columns that use a domain data type enforce the domain's constraints on `INSERT`, `UPDATE`, and cast operations.
* Domain `DEFAULT` and `CHECK` expressions cannot reference database objects such as tables, sequences, user-defined functions, or user-defined types. A domain can be based on a user-defined type such as an `ENUM`.
* The base type of a domain cannot be an array, composite, or domain data type.
## Examples
### Create a domain with a default value and constraints
The following statement creates a domain based on `DECIMAL` that defaults to `0`, disallows `NULL` values, and rejects negative values:
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> CREATE DOMAIN price AS DECIMAL DEFAULT 0 NOT NULL CHECK (VALUE >= 0);
```
### Create a domain with a named constraint
The following statement creates a domain with a `CHECK` constraint named `us_phone_format`:
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> CREATE DOMAIN us_phone AS STRING CONSTRAINT us_phone_format CHECK (VALUE ~ '^[0-9]{10}$');
```
To view the domains in the current database, use `SHOW CREATE ALL TYPES`:
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> SELECT create_statement FROM [SHOW CREATE ALL TYPES];
```
```
create_statement
-----------------------------------------------------------------------------------------------------------------
CREATE DOMAIN public.price AS DECIMAL DEFAULT 0:::DECIMAL NOT NULL CONSTRAINT price_check CHECK (value >= 0);
CREATE DOMAIN public.us_phone AS STRING CONSTRAINT us_phone_format CHECK (value ~ '^[0-9]{10}$');
(2 rows)
```
### Use a domain in a table
Use the domains created in the preceding examples as column types:
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> CREATE TABLE products (
id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
name STRING,
list_price price,
support_line us_phone
);
```
The `list_price` column inherits the domain's `DEFAULT` value:
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> INSERT INTO products (name, support_line) VALUES ('widget', '8005550100');
```
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> SELECT name, list_price, support_line FROM products;
```
```
name | list_price | support_line
---------+------------+---------------
widget | 0 | 8005550100
(1 row)
```
A value that violates the `price_check` constraint returns an error:
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> INSERT INTO products (name, list_price) VALUES ('gadget', -1.99);
```
```
ERROR: value for domain price violates check constraint "price_check"
SQLSTATE: 23514
```
The error message includes the constraint name that was specified at creation:
```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
> INSERT INTO products (name, support_line) VALUES ('gizmo', '555-0100');
```
```
ERROR: value for domain us_phone violates check constraint "us_phone_format"
SQLSTATE: 23514
```
## Known limitations
Refer to `DOMAIN`: Known limitations.
## See also
* `DOMAIN`
* `ALTER DOMAIN`
* `DROP DOMAIN`
* Data types
* Online Schema Changes