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2ef3080d0e
Ensure columns can be created when they are IDENTITY fields with the CYCLE option enabled. Fixes #4496 Ensure purely numeric comments can be saved on new columns. Fixed #4497
172 lines
7.0 KiB
ReStructuredText
172 lines
7.0 KiB
ReStructuredText
.. _column_dialog:
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**********************
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`Column Dialog`:index:
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**********************
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Use the *Column* dialog to add a column to an existing table or modify a column
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definition.
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The *Column* dialog organizes the development of a column through the following
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dialog tabs: *General*, *Definition*, and *Security*. The *SQL* tab displays the
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SQL code generated by dialog selections.
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.. image:: images/column_general.png
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:alt: Column dialog general tab
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:align: center
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Use the fields in the *General* tab to identify the column:
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* Use the *Name* field to add a descriptive name for the column. The name will
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be displayed in the *pgAdmin* tree control. This field is required.
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* Store notes about the column in the *Comment* field.
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Click the *Definition* tab to continue.
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.. image:: images/column_definition.png
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:alt: Column dialog definition tab
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:align: center
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Use the fields in the *Definition* tab to add parameters for the column. (Fields
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are disabled if inapplicable.)
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* Use the drop-down listbox next to *Data Type* to select a data type for the
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column. For more information on the data types that are supported by
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PostgreSQL, refer to Chapter 8 of the Postgres core documentation. This field
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is required.
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* Use the *Length* and *Precision* fields to specify the maximum number of
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significant digits in a numeric value, or the maximum number of characters in
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a text value.
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* Use the drop-down listbox next to *Collation* to apply a collation setting to
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the column.
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Click the *Constraints* tab to continue.
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.. image:: images/column_constraints.png
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:alt: Column dialog constraints tab
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:align: center
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Use the fields in the *Constraints* tab to specify constraints for the column.
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(Fields are disabled if inapplicable.)
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* Use the *Default Value* field to specify a default data value.
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* Move the *Not Null* switch to the *Yes* position to specify the column may not
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contain null values. The default is *No*.
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* Use the *Type* field to specify the column type (NONE/IDENTITY/GENERATED).
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The default is *NONE*.
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Click the *IDENTITY* type to create Identity column.
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.. image:: images/column_constraint_identity.png
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:alt: Column dialog constraints tab
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:align: center
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Use the following fields to create *IDENTITY* column. Identity columns are
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applicable for PG/EPAS version 10 and above.
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* Use the *Identity* field to specify ALWAYS or BY DEFAULT. This clause is
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used to determine how the sequence value is given precedence over a
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user-specified value in an INSERT statement.
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* Use the *Increment* field to specify which value is added to the current
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sequence value to create a new value.
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* Provide a value in the *Start* field to specify the beginning value of the
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sequence. The default starting value is MINVALUE for ascending sequences and
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MAXVALUE for descending ones.
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* Provide a value in the *Minimum* field to specify the minimum value a sequence
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can generate. If this clause is not supplied or NO MINVALUE is specified,
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then defaults will be used. The defaults are 1 and -263-1 for ascending and
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descending sequences, respectively.
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* Provide a value in the *Maximum* field to specify the maximum value for the
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sequence. If this clause is not supplied or NO MAXVALUE is specified, then
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default values will be used. The defaults are 263-1 and -1 for ascending and
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descending sequences, respectively.
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* Provide a value in the *Cache* field to specify how many sequence numbers are
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to be preallocated and stored in memory for faster access. The minimum value
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is 1 (only one value can be generated at a time, i.e., no cache), and this is
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also the default.
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* Move the *Cycled* switch to the *Yes* position to allow the sequence to wrap
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around when the MAXVALUE or the MINVALUE has been reached by an ascending or
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descending sequence respectively. If the limit is reached, the next number
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generated will be the MINVALUE or MAXVALUE, respectively. The default is *No*.
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Click the *GENERATED* type to create Generated column.
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.. image:: images/column_constraint_generated.png
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:alt: Column dialog constraints tab
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:align: center
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Use the following fields to create *GENERATED* column. Generated columns are
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applicable for PG/EPAS version 12 and above.
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* Use the *Expression* field to specify the generation expression. It can
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refer to other columns in the table, but not other generated columns.
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Any functions and operators used must be immutable. References to other
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tables are not allowed.
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Click the *Variables* tab to continue.
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.. image:: images/column_variables.png
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:alt: Column dialog variables tab
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:align: center
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Use the *Variables* tab to to specify the number of distinct values that may be
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present in the column; this value overrides estimates made by the ANALYZE
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command. Click the *Add* icon (+) to add a *Name*/*Value* pair:
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* Select the name of the variable from the drop-down listbox in the *Name* field.
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* Select *n_distinct* to specify the number of distinct values for the column.
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* Select *n_distinct_inherited* to specify the number of distinct values
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for the table and its children.
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* Specify the number of distinct values in the *Value* field. For more
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information, see the documentation for
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`ALTER TABLE <https://www.postgresql.org/docs/current/sql-altertable.html>`_.
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Click the *Add* icon (+) to specify each additional *Name*/*Value* pair; to
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discard a variable, click the trash icon to the left of the row and confirm
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deletion in the *Delete Row* popup.
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Click the *Security* tab to continue.
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.. image:: images/column_security.png
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:alt: Column dialog security tab
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:align: center
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Use the *Security* tab to assign attributes and define security labels. Click
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the *Add* icon (+) to add each security label selection:
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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 assign additional security labels; to discard a
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security label, click the trash icon to the left of the row and confirm deletion
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in the *Delete Row* popup.
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Click the *SQL* tab to continue.
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Your entries in the *Column* 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 user selections in
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the *Column* dialog:
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.. image:: images/column_sql.png
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:alt: Column dialog sql tab
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:align: center
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The example shown demonstrates creating a column named *territory* in the table
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named *distributors*.
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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 *Cancel* button to exit without saving work.
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* Click the *Reset* button to restore configuration parameters. |