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71 lines
2.7 KiB
ReStructuredText
71 lines
2.7 KiB
ReStructuredText
.. _domain_constraint_dialog:
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**********************************
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`Domain Constraints Dialog`:index:
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**********************************
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Use the *Domain Constraints* dialog to create or modify a domain constraint. A
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domain constraint confirms that the values provided for a domain meet a defined
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criteria. The *Domain Constraints* dialog implements options of the ALTER DOMAIN
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command.
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The *Domain Constraints* dialog organizes the development of a domain constraint
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through the following dialog tabs: *General* and *Definition*. The *SQL* tab
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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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:align: center
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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
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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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:align: center
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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
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specifies a constraint that the domain must satisfy. A constraint must produce
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a Boolean result; include the key word VALUE to refer to the value being
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tested. Only those expressions that evaluate to TRUE or UNKNOWN will succeed.
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A CHECK expression cannot contain subqueries or refer to variables other than
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VALUE. If a domain has multiple CHECK constraints, they will be tested in
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alphabetical order.
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* Move the *Validate?* switch to the *No* position to mark the constraint NOT
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VALID. If the constraint is marked NOT VALID, the constraint will not be
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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
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example below). Use the *SQL* tab for review; revisit or switch tabs to make any
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changes to the SQL command.
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Example
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*******
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The following is an example of the sql command generated by user selections in
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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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:align: center
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The example shown demonstrates creating a domain constraint on the domain
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*timesheets* named *weekday*. It constrains a value equal to *Friday*.
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* Click the *Info* button (i) to access online help.
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* Click the *Save* button to save work.
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* Click the *Close* button to exit without saving work.
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* Click the *Reset* button to restore configuration parameters.
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