Unique Constraints

Unique constraints are a combination of values (represented by Table columns) that uniquely identify a row in the Table. You can have several unique constraints in a Table, one of which can be separately identified as the Primary Key of the Table.

Access     In diagram or Project Browser | Right-click on Table | Features & Properties | Operations > Constraint | Add New Constraint (Ctrl+N)

Create a Constraint

Step

Action

See also

1

On the Constraint tab of the Columns and Constraints screen, a new constraint is automatically created and assigned the default constraint name and a Type of index.

Overtype the constraint name with a name that identifies this as a unique constraint.

 

 

2

In the Type field, change the value from index to unique.

 

 

3

If you prefer, type an alias for the constraint, in the Alias field.

The Columns field is read-only; it is populated with the columns that you assign to the Involved Columns tab (step 4).

 

 

4

The Available Columns panel lists the columns defined for the Table (on the Columns tab).

For each column to assign to the constraint, either:

·Right-click on the column name and select Assign column '<name>' or
·Press Ctrl+left arrow or
·Double-click on the column name

 

The column name is transferred to the Involved Columns tab.

 

 

5

If you do not want the assigned column in the Involved Columns tab, either:

·Right-click on it and select Unassign column '<name>', or
·Press Ctrl+right arrow, or
·Double-click on the column name

 

 

6

If you have a number of columns in the constraint, you can rearrange the sequence by right-clicking on the column to move and selecting either:

·Move column '<name>' up   (Ctrl+Up arrow) or
·Move column '<name>' down   (Ctrl+Down arrow)

 

 

7

If necessary, you can type a formatted comment in the field on the Notes tab.

 

 

8

(On the Columns and Constraints dialog) Click on the Close button.

 

 

Delete a unique constraint

If you do not want to keep a unique constraint, either:

·Right-click on it in the list and select Delete constraint '<name>', or
·Click on the item and press Ctrl+D

 

The constraint is immediately deleted.

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