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49 lines
2.7 KiB
ReStructuredText
49 lines
2.7 KiB
ReStructuredText
.. _domain_constraint_dialog:
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*****************************
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The Domain Constraints Dialog
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Use the *Domain Constraints* dialog to create or modify a domain constraint. A domain constraint confirms that the values provided for a domain meet a defined criteria. The *Domain Constraints* dialog implements options of the ALTER DOMAIN command.
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The *Domain Constraints* dialog organizes the development of a domain constraint through the following dialog tabs: *General* and *Definition*. The *SQL* tab displays the SQL code generated by dialog selections.
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.. image:: images/domain_constraint_general.png
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:alt: Domain constraint dialog general tab
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Use the fields in the *General* tab to identify the domain constraint:
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* Use the *Name* field to add a descriptive name for the constraint. The name will be displayed in the *pgAdmin* tree control.
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* Store notes about the constraint in the *Comment* field.
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Click the *Definition* tab to continue.
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.. image:: images/domain_constraint_definition.png
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:alt: Domain constraint dialog general tab
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Use the fields in the *Definition* tab to define the domain constraint:
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* Use the *Check* field to provide a CHECK expression. A CHECK expression specifies a constraint that the domain must satisfy. A constraint must produce a Boolean result; include the key word VALUE to refer to the value being tested. Only those expressions that evaluate to TRUE or UNKNOWN will succeed. A CHECK expression cannot contain subqueries or refer to variables other than VALUE. If a domain has multiple CHECK constraints, they will be tested in alphabetical order.
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* Move the *Validate?* switch to the *No* position to mark the constraint NOT VALID. If the constraint is marked NOT VALID, the constraint will not be applied to existing column data. The default value is *Yes*.
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Click the *SQL* tab to continue.
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Your entries in the *Domain Constraints* 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.
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**Example**
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The following is an example of the sql command generated by user selections in the *Domain Constraints* dialog:
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.. image:: images/domain_constraint_sql.png
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:alt: Domain constraint dialog general tab
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The example shown demonstrates creating a domain constraint on the domain *timesheets* named *weekday*. It constrains a value to equal *Friday*.
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* 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.
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* Click the *Save* button to save work.
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* Click the *Cancel* button to exit without saving work.
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* Click the *Reset* button to restore configuration parameters.
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