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128 lines
5.1 KiB
ReStructuredText
128 lines
5.1 KiB
ReStructuredText
.. _domain_dialog:
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**********************
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`Domain Dialog`:index:
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**********************
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Use the *Domain* dialog to define a domain. A domain is a data type definition
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that may constrain permissible values. Domains are useful when you are creating
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multiple tables that contain comparable columns; you can create a domain that
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defines constraints that are common to the columns and re-use the domain
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definition when creating the columns, rather than individually defining each
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set of constraints.
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The *Domain* dialog organizes the development of a domain through the following
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tabs: *General*, *Definition*, *Constraints*, and *Security*. The *SQL* tab
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displays the SQL code generated by dialog selections.
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.. image:: images/domain_general.png
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:alt: Domain dialog general tab
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:align: center
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Use the fields on the *General* tab to identify a domain:
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* Use the *Name* field to add a descriptive name for the domain. The name will
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be displayed in the *pgAdmin* tree control.
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* Use the drop-down listbox next to *Owner* to select a role that will own the
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domain.
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* Select the name of the schema in which the domain will reside from the
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drop-down listbox in the *Schema* field.
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* Store notes about the domain in the *Comment* field.
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Click the *Definition* tab to continue.
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.. image:: images/domain_definition.png
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:alt: Domain dialog definition tab
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:align: center
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Use the fields in the *Definition* tab to describe the domain:
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* Use the drop-down listbox next to *Base type* to specify a data type.
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* Use the context-sensitive *Length* field to specify a numeric length for a
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numeric type.
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* Use the context-sensitive *Precision* field to specify the total count of
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significant digits for a numeric type.
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* Specify a default value for the domain data type in the *Default* field. The
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data type of the default expression must match the data type of the domain. If
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no default value is specified, then the default value is the null value.
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* Move the *Not Null* switch to specify the values of this domain are prevented
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from being null.
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* Use the drop-down listbox next to *Collation* to apply a collation cast. If
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no collation is specified, the underlying data type's default collation is
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used. The underlying type must be collatable if COLLATE is specified.
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Click the *Constraints* tab to continue.
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.. image:: images/domain_constraints.png
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:alt: Domain dialog constraints tab
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:align: center
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Use the fields in the *Constraints* tab to specify rules for the domain. Click
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the *Add* icon (+) to set constraints:
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* Use the *Name* field to specify a name for the constraint.
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* Use the *Check* field to provide an expression for the constraint.
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* Use the *Validate* checkbox to determine whether the constraint will be
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validated. The default checkbox is checked and sets a validation requirement.
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A CHECK clause specifies an integrity test which values of the domain must
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satisfy. Each constraint must be an expression that produces a Boolean result.
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Use the key word VALUE to refer to the value being tested. Expressions
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evaluating to TRUE or UNKNOWN succeed. If the expression produces a FALSE
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result, an error is reported and the value is not allowed to be converted to
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the domain type. A CHECK expression cannot contain subqueries nor refer to
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variables other than VALUE. If a domain has multiple CHECK constraints, they
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will be tested in alphabetical order by name.
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Click the *Add* icon (+) to set additional constraints; to discard a constraint,
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click the trash icon to the left of the row and confirm deletion in the *Delete
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Row* popup.
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Click the *Security* tab to continue.
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.. image:: images/domain_security.png
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:alt: Domain dialog security tab
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:align: center
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Use the *Security Labels* panel to assign security labels. Click the *Add* icon
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(+) to add a label:
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* Specify a security label provider in the *Provider* field. The named provider
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must be loaded and must consent to the proposed labeling operation.
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* Specify a a security label in the *Security Label* field. The meaning of a
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given label is at the discretion of the label provider. PostgreSQL places no
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restrictions on whether or how a label provider must interpret security
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labels; it merely provides a mechanism for storing them.
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Click the *Add* icon (+) to specify each additional label; to discard a label,
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click the trash icon to the left of the row and confirm deletion in the *Delete
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Row* popup.
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Click the *SQL* tab to continue.
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Your entries in the *Domain* dialog generate a SQL command (see an example
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below). Use the *SQL* tab for review; revisit or switch tabs to make any changes
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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 selections made in
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the *Domain* dialog:
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.. image:: images/domain_sql.png
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:alt: Domain dialog sql tab
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:align: center
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The example shown demonstrates creating a domain named *postal_code* that
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confirms that the value entered is in proper format.
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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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