Column Dialog v9
Use the Column
dialog to add a column to an existing table or modify a column definition.
The Column
dialog organizes the development of a column through the following dialog tabs: General
, Definition
, and Security
. The SQL
tab displays the SQL code generated by dialog selections.
Use the fields in the General
tab to identify the column:
- Use the
Name
field to add a descriptive name for the column. The name will be displayed in theBrowser
tree control. This field is required. - Store notes about the column in the
Comment
field.
Click the Definition
tab to continue.
Use the fields in the Definition
tab to add parameters for the column. (Fields are disabled if inapplicable.)
- Use the drop-down listbox next to
Data Type
to select a data type for the column. For more information on the data types that are supported by PostgreSQL, refer to Chapter 8 of the Postgres core documentation. This field is required. - Use the
Length/Precision
andScale
fields to specify the maximum number of significant digits in a numeric value, or the maximum number of characters in a text value. - Use the drop-down listbox next to
Collation
to apply a collation setting to the column.
Click the Constraints
tab to continue.
Use the fields in the Constraints
tab to specify constraints for the column. (Fields are disabled if inapplicable.)
- Use the
Default Value
field to specify a default data value. - Move the
Not Null
switch to theYes
position to specify the column may not contain null values. The default isNo
. - Use the
Type
field to specify the column type (NONE/IDENTITY/GENERATED). The default isNONE
.
Click the IDENTITY
type to create Identity column.
Use the following fields to create IDENTITY
column. Identity columns are applicable for PG/EPAS version 10 and above.
- Use the
Identity
field to specify ALWAYS or BY DEFAULT. This clause is used to determine how the sequence value is given precedence over a user-specified value in an INSERT statement. - Use the
Increment
field to specify which value is added to the current sequence value to create a new value. - Provide a value in the
Start
field to specify the beginning value of the sequence. The default starting value is MINVALUE for ascending sequences and MAXVALUE for descending ones. - Provide a value in the
Minimum
field to specify the minimum value a sequence can generate. If this clause is not supplied or NO MINVALUE is specified, then defaults will be used. The defaults are 1 and -263-1 for ascending and descending sequences, respectively. - Provide a value in the
Maximum
field to specify the maximum value for the sequence. If this clause is not supplied or NO MAXVALUE is specified, then default values will be used. The defaults are 263-1 and -1 for ascending and descending sequences, respectively. - Provide a value in the
Cache
field to specify how many sequence numbers are to be preallocated and stored in memory for faster access. The minimum value is 1 (only one value can be generated at a time, i.e., no cache), and this is also the default. - Move the
Cycled
switch to theYes
position to allow the sequence to wrap around when the MAXVALUE or the MINVALUE has been reached by an ascending or descending sequence respectively. If the limit is reached, the next number generated will be the MINVALUE or MAXVALUE, respectively. The default isNo
.
Click the GENERATED
type to create Generated column.
Use the following fields to create GENERATED
column. Generated columns are applicable for PG/EPAS version 12 and above.
- Use the
Expression
field to specify the generation expression. It can refer to other columns in the table, but not other generated columns. Any functions and operators used must be immutable. References to other tables are not allowed.
Click the Variables
tab to continue.
Use the Variables
tab to specify the number of distinct values that may be present in the column; this value overrides estimates made by the ANALYZE command. Click the Add
icon (+) to add a Name
/Value
pair:
Select the name of the variable from the drop-down listbox in the
Name
field.- Select
n_distinct
to specify the number of distinct values for the column. - Select
n_distinct_inherited
to specify the number of distinct values for the table and its children.
- Select
Specify the number of distinct values in the
Value
field. For more information, see the documentation for ALTER TABLE.
Click the Add
icon (+) to specify each additional Name
/Value
pair; to discard a variable, click the trash icon to the left of the row and confirm deletion in the Delete Row
popup.
Click the Security
tab to continue.
Use the Security
tab to assign attributes and define security labels. Click the Add
icon (+) to add each security label selection:
- Specify a security label provider in the
Provider
field. The named provider must be loaded and must consent to the proposed labeling operation. - Specify a a security label in the
Security Label
field. The meaning of a given label is at the discretion of the label provider. PostgreSQL places no restrictions on whether or how a label provider must interpret security labels; it merely provides a mechanism for storing them.
Click the Add
icon (+) to assign additional security labels; to discard a security label, click the trash icon to the left of the row and confirm deletion in the Delete Row
popup.
Click the SQL
tab to continue.
Your entries in the Column
dialog generate a SQL command (see an example below). Use the SQL
tab for review; revisit or switch tabs to make any changes to the SQL command.
Example
The following is an example of the sql command generated by user selections in the Column
dialog:
The example shown demonstrates creating a column named territory
in the table named distributors
.
- Click the
Info
button (i) to access online help. View context-sensitive help in theTabbed browser
, where a new tab displays the PostgreSQL core documentation. - Click the
Save
button to save work. - Click the
Cancel
button to exit without saving work. - Click the
Reset
button to restore configuration parameters.