.. _domain_dialog:

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The Domain Dialog
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Use the *Domain* dialog to define a domain. A domain is a data type definition that may constrain permissible values. Domains are useful when you are creating multiple tables that contain comparable columns; you can create a domain that defines constraints that are common to the columns and re-use the domain definition when creating the columns, rather than individually defining each set of constraints.  

The *Domain* dialog organizes the development of a domain through the following tabs: *General*, *Definition*, *Constraints*, and *Security*. The *SQL* tab displays the SQL code generated by dialog selections. 

.. image:: images/domain_general.png

Use the fields on the *General* tab to identify a domain:

* Use the *Name* field to add a descriptive name for the domain. The name will be displayed in the *pgAdmin* tree control.
* Use the drop-down listbox next to *Owner* to select a role that will own the domain.
* Select the name of the schema in which the domain will reside from the drop-down listbox in the *Schema* field.
* Store notes about the domain in the *Comment* field.

Click the *Definition* tab to continue.

.. image:: images/domain_definition.png

Use the fields in the *Definition* tab to describe the domain:

* Use the drop-down listbox next to *Base type* to specify a data type.
* Use the context-sensitive *Length* field to specify a numeric length for a numeric type.
* Use the context-sensitive *Precision* field to specify the total count of significant digits for a numeric type.
* Specify a default value for the domain data type in the *Default* field. The data type of the default expression must match the data type of the domain. If no default value is specified, then the default value is the null value.
* Move the *Not Null* switch to specify the values of this domain are prevented from being null.
* Use the drop-down listbox next to *Collation* to apply a collation cast. If no collation is specified, the underlying data type's default collation is used. The underlying type must be collatable if COLLATE is specified.   

Click the *Constraints* tab to continue.

.. image:: images/domain_constraints.png

Use the fields in the *Constraints* tab to specify rules for the domain. Click the *Add* icon (+) to set constraints:

* Use the *Name* field to specify a name for the constraint.
* Use the *Check* field to provide an expression for the constraint.
* Use the *Validate* checkbox to determine whether the constraint will be validated. The default checkbox is checked and sets a validation requirement. 

A CHECK clause specifies an integrity test which values of the domain must satisfy. Each constraint must be an expression that produces a Boolean result. Use the key word VALUE to refer to the value being tested. Expressions evaluating to TRUE or UNKNOWN succeed. If the expression produces a FALSE result, an error is reported and the value is not allowed to be converted to the domain type.  A CHECK expression cannot contain subqueries nor refer to variables other than VALUE.  If a domain has multiple CHECK constraints, they will be tested in alphabetical order by name. 

Click the *Add* icon (+) to set additional constraints; to discard a constraint, click the trash icon to the left of the row and confirm deletion in the *Delete Row* popup.

Click the *Security* tab to continue.

.. image:: images/domain_security.png

Use the *Security Labels* panel to assign security labels. Click the *Add* icon (+) to add a label:

* Specify a security label provider in the *Provider* field. The named provider must be loaded and must consent to the proposed labeling operation.
* Specify a a security label in the *Security Label* field. The meaning of a given label is at the discretion of the label provider. PostgreSQL places no restrictions on whether or how a label provider must interpret security labels; it merely provides a mechanism for storing them.

Click the *Add* icon (+) to specify each additional label; to discard a label, click the trash icon to the left of the row and confirm deletion in the *Delete Row* popup.

Click the *SQL* tab to continue.

Your entries in the *Domain* dialog generate a SQL command (see an example below). Use the *SQL* tab for review; revisit or switch tabs to make any changes to the SQL command.

**Example**

The following is an example of the sql command generated by selections made in the *Domain* dialog: 

.. image:: images/domain_sql.png

The example shown demonstrates creating a domain named *minimum-wage* that confirms that the value entered is greater than or equal to *7.25*. 
 
* Click the *Info* button (i) to access online help. View context-sensitive help in the *Tabbed browser*, where a new tab displays the PostgreSQL core documentation.
* Click the *Save* button to save work.
* Click the *Cancel* button to exit without saving work.
* Click the *Reset* button to restore configuration parameters.