Domain Constraints Dialog v8
Use the Domain Constraints
dialog to create or modify a domain constraint. A domain constraint confirms that the values provided for a domain meet a defined criteria. The Domain Constraints
dialog implements options of the ALTER DOMAIN command.
The Domain Constraints
dialog organizes the development of a domain constraint through the following dialog tabs: General
and Definition
. The SQL
tab displays the SQL code generated by dialog selections.
Use the fields in the General
tab to identify the domain constraint:
- Use the
Name
field to add a descriptive name for the constraint. The name will be displayed in theBrowser
tree control. - Store notes about the constraint in the
Comment
field.
Click the Definition
tab to continue.
Use the fields in the Definition
tab to define the domain constraint:
- Use the
Check
field to provide a CHECK expression. A CHECK expression specifies a constraint that the domain must satisfy. A constraint must produce a Boolean result; include the key word VALUE to refer to the value being tested. Only those expressions that evaluate to TRUE or UNKNOWN will succeed. A CHECK expression cannot contain subqueries or refer to variables other than VALUE. If a domain has multiple CHECK constraints, they will be tested in alphabetical order. - Move the
Validate?
switch to theNo
position to mark the constraint NOT VALID. If the constraint is marked NOT VALID, the constraint will not be applied to existing column data. The default value isYes
.
Click the SQL
tab to continue.
Your entries in the Domain Constraints
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 Domain Constraints
dialog:
The example shown demonstrates creating a domain constraint on the domain timesheets
named weekday
. It constrains a value to equal Friday
.
- 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.