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A check constraint is the most generic constraint type. It allows you to specify that the value in a certain column must satisfy a Boolean (truth-value) expression.

The Check Properties editor allows you to add a new check constraint or edit an existing one. This dialog can be invoked from Table Editor, or via the popup menu of the corresponding nodes of the explorer tree.

Checks are created within Check Properties. In order to run the wizard you should either

•	open the table in Table Editor and the Checks tab there;

•	press the Insert key or select the Add New Check... item from the popup menu (alternatively, you may use the corresponding link of the Navigation Bar)

•	select the table in the explorer tree and use the Create New Check... popup menu item

•	select the table Checks node or any check within the table in the explorer tree and use the Add New Check... popup menu item.

Checks are edited within the Check Properties dialog window. In order to open the dialog you should either

•	open the table in Table Editor the Checks tab there;

•	press the Enter key or select the Edit Check item from the popup menu (alternatively, you may use the corresponding link of the Navigation Bar)

•	select the check to edit in the explorer tree and use the Edit Check popup menu item.

You can change the name of the check using the Rename Check dialog. To open the dialog you should either

•	select the check to rename in the explorer tree;

•	select the Rename Check item from the popup menu

•	open the table in Table Editor and the Checks tab there;

•	select the check to rename;

•	select the Rename Check item from the popup menu (alternatively, you may use the corresponding link of the Navigation Bar).

To drop the check:

•	select the check to drop in the explorer tree;

•	select the Drop Check item from the popup menu

•	open the table in Table Editor and the Checks tab there;

•	press the Delete key or select the Drop Check item from the popup menu (alternatively, you may use the corresponding link of the Navigation Bar)

and confirm dropping in the dialog window.

Name

The name of the check constraint.

Comment

This field contains an optional text describing the check.

OID

This field stores the check OID (object identifier). This is a serial number that is automatically added by PostgreSQL to all checks.

Condition

Specify an expression producing a Boolean result which new or updated rows must satisfy for an insert or update operation to succeed. Expressions evaluating to True or Unknown succeed. In case any row of an insert or update operation produce a FALSE result an error exception is raised and the insert or update does not alter the database.

Not validated

Turn this option ON to skip a scan of the table to verify that all existing rows in the table satisfy the new constraint. In this case the constraint will be applied against new inserts or updates. The database will not assume that the constraint holds for all rows in the table, until it will be validated manually via popup menu of the Checks tab in the Table Editor. Icons for not validated constraints are marked with a red exclamation mark in GUI.

Not enforced

Turn this option ON to prevent the database system from checking the constraint. It is then up to the application code to ensure that the constraints are satisfied. The database system might still assume that the data actually satisfies the constraint for optimization decisions where this does not affect the correctness of the result. Not enforced constraints can be useful as documentation if the actual checking of the constraint at run time is too expensive. Leave this option OFF to oblige the database system to ensure that the constraint is satisfied, by checking the constraint at appropriate times (after each statement or at the end of the transaction, as appropriate). Not enforced check constraints are displayed with a grayscale icon in the GUI.