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Adding a New Table Constraint

In this example, you add a table constraint to the purchase_orders table that you created in "Example: Creating a Table" on page 8-11. To enforce the rule that the po_ date_received valuc must be either the same day as. or later than. the value of

po_

datę, you add a chcck constraint.

To add a table constraint to the PURCHASE_ORDERS table:

1.    Navigatc to the PURCHASE_ORDERS table in the HR schema, following the instructions in "Viewing Tables" on page 8-10.

2.    Right-click the PURCHAS E_ORDERS table and select Edit.

The Edit Table dialog box appears.

3.    Under the Search box, click Check Constraints.

4.    To the right of the Check Constraints section, click Add.

5.    In the Name field, entcr PO_CHECK_RCVD_DATE. This constraint namc that you specify will overwrite the system-assigned default name that appears in the Check Constraints text box above the Name field.

6.    In the Condition field, enter the following condition for this constraint:

PO_DATE_RECEIVED >= PO_DATE

This expression indicates that PO_DATE_RECEIVED must be greater than or equal to

PO_DATE. For datę columns, this is cquivalcnt to stating that PO_DATE_RECEIVED must be on the same day as, or later than, PO_DATE.