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105 lines
4.4 KiB
ReStructuredText
105 lines
4.4 KiB
ReStructuredText
.. _exclusion_constraint_dialog:
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************************************
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`Exclusion Constraint Dialog`:index:
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************************************
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Use the *Exclusion constraint* dialog to define or modify the behavior of an
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exclusion constraint. An exclusion constraint guarantees that if any two rows
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are compared on the specified column or expression (using the specified
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operator), at least one of the operator comparisons will return false or null.
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The *Exclusion constraint* dialog organizes the development of an exclusion
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constraint through the following dialog tabs: *General*, *Definition*, and
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*Columns*. The *SQL* tab displays the SQL code generated by dialog selections.
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.. image:: images/exclusion_constraint_general.png
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:alt: Exclusion constraint dialog general tab
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:align: center
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Use the fields in the *General* tab to identify the exclusion constraint:
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* Use the *Name* field to provide a descriptive name for the exclusion
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constraint. The name will be displayed in the *pgAdmin* tree control.
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Click the *Definition* tab to continue.
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.. image:: images/exclusion_constraint_definition.png
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:alt: Exclusion constraint dialog definition tab
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:align: center
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Use the fields in the *Definition* tab to define the exclusion constraint:
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* Use the drop-down listbox next to *Tablespace* to select the tablespace in
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which the index associated with the exclude constraint will reside.
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* Use the drop-down listbox next to *Access method* to specify the type of
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index that will be used when implementing the exclusion constraint:
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* Select *gist* to specify a GiST index.
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* Select *spgist* to specify a space-partitioned GiST index.
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* Select *btree* to specify a B-tree index.
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* Select *hash* to specify a hash index.
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* Use the *Fill Factor* field to specify a fill factor for the table and
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associated index. The fill factor is a percentage between 10 and 100. 100
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(complete packing) is the default.
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* Move the *Deferrable?* switch to the *Yes* position to specify that the
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timing of the constraint is deferrable, and can be postponed until the end of
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the statement. The default is *No*.
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* If enabled, move the *Deferred?* switch to the *Yes* position to specify the
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timing of the constraint is deferred to the end of the statement. The default
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is *No*.
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* Use the *Constraint* field to provide a condition that a row must satisfy to
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be included in the table.
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Click the *Columns* tab to continue.
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.. image:: images/exclusion_constraint_columns.png
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:alt: Exclusion constraint dialog columns tab
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:align: center
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Use the fields in the *Columns* tab to specify the column(s) or expression(s)
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to which the constraint applies. Use the *Is expression ?* switch to enable
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expression text input. Use the drop-down listbox next to *Column*
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to select a column. Once the *Column* is selected or the *Expression* is
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entered then click the *Add* icon (+) to provide details of the action on the
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column/expression:
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* The *Col/Exp* field is populated with the selection made in the *Column*
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drop-down listbox or the *Expression* entered.
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* If applicable, use the drop-down listbox in the *Operator class* to specify
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the operator class that will be used by the index for the column.
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* Move the *DESC* switch to *DESC* to specify a descending sort order. The
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default is *ASC* which specifies an ascending sort order.
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* Use the *NULLs order* column to specify the placement of NULL values (when
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sorted). Specify *FIRST* or *LAST*.
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* Use the drop-down list next to *Operator* to specify a comparison or
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conditional operator.
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Use *Include columns* field to specify columns for *INCLUDE* clause of the
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constraint. This option is available in Postgres 11 and later.
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Click the *SQL* tab to continue.
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Your entries in the *Exclusion Constraint* dialog generate a SQL command (see
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an example below). Use the *SQL* tab for review; revisit or switch tabs to make
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any 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 *Exclusion Constraint* dialog:
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.. image:: images/exclusion_constraint_sql.png
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:alt: Exclusion constraint dialog sql tab
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:align: center
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The example shown demonstrates creating an exclusion constraint named
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*ex_dept_no*. The constraint uses a btree index.
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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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