Konsistenz von Beziehungen bei MySQL V

mysql> select * from Abteilungen; Empty set (0.02 sec) mysql> insert into Abteilungen values ('SAI', -> 'Abteilung Angewandte Informationsverarbeitung', -> NULL); Query OK, 1 row affected (0.00 sec) mysql> insert into Angestellte values -> ('swg', 'Franz Schweiggert', 'SAI'); Query OK, 1 row affected (0.01 sec) mysql> update Abteilungen set chef = 'swg' -> where abtid = 'SAI'; Query OK, 1 row affected (0.07 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> delete from Abteilungen where abtid = 'SAI'; ERROR 1217: Cannot delete or update a parent row: a foreign key constraint fails mysql> delete from Angestellte where persid = 'swg'; Query OK, 1 row affected (0.00 sec) mysql> select abtid, chef from Abteilungen; +-------+------+ | abtid | chef | +-------+------+ | SAI | NULL | +-------+------+ 1 row in set (0.01 sec) mysql>