====== LU08d – Fremdschlüssel nachträglich hinzufügen (ALTER TABLE) ======

Falls deine Tabellen schon ohne FK existieren, rüstest du die Constraints so nach:

<WRAP center box 80% round><code sql>
ALTER TABLE Country
  ADD CONSTRAINT fk_country_continent
  FOREIGN KEY (ContinentID)
  REFERENCES Continent(ContinentID)
  ON DELETE RESTRICT
  ON UPDATE RESTRICT;

ALTER TABLE Trip
  ADD CONSTRAINT fk_trip_country
  FOREIGN KEY (CountryID)
  REFERENCES Country(CountryID)
  ON DELETE RESTRICT
  ON UPDATE RESTRICT;
</code></WRAP>

**Tipp:** Effektive Constraint-Namen anzeigen:
<WRAP center box 80% round><code sql>
SHOW CREATE TABLE Country\G
SHOW CREATE TABLE Trip\G
</code></WRAP>