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| <section id="column-dialog">
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| <span id="id1"></span><h1><span class="target" id="index-0"></span>Column Dialog<a class="headerlink" href="#column-dialog" title="Link to this heading">¶</a></h1>
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| <p>Use the <em>Column</em> dialog to add a column to an existing table or modify a column
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| definition.</p>
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| <p>The <em>Column</em> dialog organizes the development of a column through the following
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| dialog tabs: <em>General</em>, <em>Definition</em>, and <em>Security</em>. The <em>SQL</em> tab displays the
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| SQL code generated by dialog selections.</p>
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| <img alt="Column dialog general tab" class="align-center" src="_images/column_general.png" />
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| <p>Use the fields in the <em>General</em> tab to identify the column:</p>
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| <ul class="simple">
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| <li><p>Use the <em>Name</em> field to add a descriptive name for the column. The name will
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| be displayed in the <em>pgAdmin</em> tree control. This field is required.</p></li>
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| <li><p>Store notes about the column in the <em>Comment</em> field.</p></li>
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| </ul>
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| <p>Click the <em>Definition</em> tab to continue.</p>
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| <img alt="Column dialog definition tab" class="align-center" src="_images/column_definition.png" />
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| <p>Use the fields in the <em>Definition</em> tab to add parameters for the column. (Fields
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| are disabled if inapplicable.)</p>
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| <ul class="simple">
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| <li><p>Use the drop-down listbox next to <em>Data Type</em> 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.</p></li>
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| <li><p>Use the <em>Length/Precision</em> and <em>Scale</em> 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.</p></li>
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| <li><p>Use the drop-down listbox next to <em>Collation</em> to apply a collation setting to
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| the column.</p></li>
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| <li><p>Use the drop-down listbox next to <em>Compression</em> to set the compression method
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| for the column. Compression is supported only for variable-width data types,
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| and is used only when the column’s storage mode is main or extended. This
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| option is available from v14 and above.</p></li>
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| <li><p>Use the drop-down listbox next to <em>Storage</em> to set the storage mode for the
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| column. This option is available from v16 and above.</p></li>
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| </ul>
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| <p>Click the <em>Constraints</em> tab to continue.</p>
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| <img alt="Column dialog constraints tab" class="align-center" src="_images/column_constraints.png" />
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| <p>Use the fields in the <em>Constraints</em> tab to specify constraints for the column.
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| (Fields are disabled if inapplicable.)</p>
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| <ul class="simple">
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| <li><p>Use the <em>Default Value</em> field to specify a default data value.</p></li>
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| <li><p>Move the <em>Not Null</em> switch to the <em>Yes</em> position to specify the column may not
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| contain null values. The default is <em>No</em>.</p></li>
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| <li><p>Use the <em>Type</em> field to specify the column type (NONE/IDENTITY/GENERATED).
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| The default is <em>NONE</em>.</p></li>
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| </ul>
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| <p>Click the <em>IDENTITY</em> type to create Identity column.</p>
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| <img alt="Column dialog constraints tab" class="align-center" src="_images/column_constraint_identity.png" />
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| <p>Use the following fields to create <em>IDENTITY</em> column. Identity columns are
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| applicable for PG/EPAS version 10 and above.</p>
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| <ul class="simple">
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| <li><p>Use the <em>Identity</em> 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.</p></li>
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| <li><p>Use the <em>Increment</em> field to specify which value is added to the current
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| sequence value to create a new value.</p></li>
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| <li><p>Provide a value in the <em>Start</em> 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.</p></li>
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| <li><p>Provide a value in the <em>Minimum</em> 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.</p></li>
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| <li><p>Provide a value in the <em>Maximum</em> 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.</p></li>
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| <li><p>Provide a value in the <em>Cache</em> 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.</p></li>
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| <li><p>Move the <em>Cycled</em> switch to the <em>Yes</em> 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 <em>No</em>.</p></li>
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| </ul>
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| <p>Click the <em>GENERATED</em> type to create Generated column.</p>
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| <img alt="Column dialog constraints tab" class="align-center" src="_images/column_constraint_generated.png" />
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| <p>Use the following fields to create <em>GENERATED</em> column. Generated columns are
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| applicable for PG/EPAS version 12 and above.</p>
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| <ul class="simple">
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| <li><p>Use the <em>Expression</em> 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.</p></li>
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| </ul>
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| <p>Click the <em>Variables</em> tab to continue.</p>
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| <img alt="Column dialog variables tab" class="align-center" src="_images/column_variables.png" />
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| <p>Use the <em>Variables</em> tab 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 <em>Add</em> icon (+) to add a <em>Name</em>/<em>Value</em> pair:</p>
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| <ul>
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| <li><p>Select the name of the variable from the drop-down listbox in the <em>Name</em> field.</p>
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| <blockquote>
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| <div><ul class="simple">
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| <li><p>Select <em>n_distinct</em> to specify the number of distinct values for the column.</p></li>
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| <li><p>Select <em>n_distinct_inherited</em> to specify the number of distinct values
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| for the table and its children.</p></li>
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| </ul>
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| </div></blockquote>
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| </li>
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| <li><p>Specify the number of distinct values in the <em>Value</em> field. For more
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| information, see the documentation for
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| <a class="reference external" href="https://www.postgresql.org/docs/current/sql-altertable.html">ALTER TABLE</a>.</p></li>
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| </ul>
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| <p>Click the <em>Add</em> icon (+) to specify each additional <em>Name</em>/<em>Value</em> 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 <em>Delete Row</em> popup.</p>
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| <p>Click the <em>Security</em> tab to continue.</p>
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| <img alt="Column dialog security tab" class="align-center" src="_images/column_security.png" />
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| <p>Use the <em>Security</em> tab to assign attributes and define security labels. Click
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| the <em>Add</em> icon (+) to add each security label selection:</p>
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| <ul class="simple">
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| <li><p>Specify a security label provider in the <em>Provider</em> field. The named provider
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| must be loaded and must consent to the proposed labeling operation.</p></li>
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| <li><p>Specify a a security label in the <em>Security Label</em> 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.</p></li>
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| </ul>
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| <p>Click the <em>Add</em> 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 <em>Delete Row</em> popup.</p>
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| <p>Click the <em>SQL</em> tab to continue.</p>
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| <p>Your entries in the <em>Column</em> dialog generate a SQL command (see an example
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| below). Use the <em>SQL</em> tab for review; revisit or switch tabs to make any changes
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| to the SQL command.</p>
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| <section id="example">
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| <h2>Example<a class="headerlink" href="#example" title="Link to this heading">¶</a></h2>
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| <p>The following is an example of the sql command generated by user selections in
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| the <em>Column</em> dialog:</p>
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| <img alt="Column dialog sql tab" class="align-center" src="_images/column_sql.png" />
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| <p>The example shown demonstrates creating a column named <em>sal</em> in the table
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| named <em>jobhist</em>.</p>
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| <ul class="simple">
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| <li><p>Click the <em>Info</em> button (i) to access online help.</p></li>
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| <li><p>Click the <em>Save</em> button to save work.</p></li>
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| <li><p>Click the <em>Close</em> button to exit without saving work.</p></li>
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| <li><p>Click the <em>Reset</em> button to restore configuration parameters.</p></li>
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| </ul>
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| </section>
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| </section>
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| <h3><a href="index.html">Table of Contents</a></h3>
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| <li><a class="reference internal" href="#">Column Dialog</a><ul>
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| <li><a class="reference internal" href="#example">Example</a></li>
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