Variable Constraint Messages: Example 3

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In the Travel Agency, the business rule: "The return date of a scheduled tour must match the preset duration of the tour" is implemented by a corrective constraint:

UPDATE    schedtour st

SET    st.return_date =


   SELECT    st.start_date + t.num_days - 1

   FROM    tour t

   WHERE    t.destination =    st.destination

   AND    t.tour_type = st.tour_type


For this constraint, you may specify the message:

The scheduled tour to <st.destination.value> on <st.start_date.value> ends on <st.return_date.value>.

This will lead to an information message at run-time.