Propagation constraint: Difference between revisions

Revision as of 11:01, 21 February 2007

Revision as of 15:01, 27 February 2007

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* Restricted Delete - the user cannot delete the target row until all rows that point to it (via [[foreign key]]s) have been deleted. This means that all Housewares employees would need to be deleted by the user before removing the department from the departmental table.

* Cascades Delete - can delete the target row and all rows that point to it (via foreign keys) are also deleted. The process is the same as a restricted delete, except that the RDBMS would delete the Houseware employees automatically before removing the department.

* Nullifies Delete - can delete the target row and all foreign keys (pointing to it) are set to [[Null (SQL)|null]]. In this case, after removing the housewares department, employees who worked in this department would not have a [[Null (SQL)|NULL]] or (unknown) value for their department.

==Bibliography==