DELETE Rule (delete_rule) 

The DELETE rule (delete_rule) defines the effects that deleting a row in the referenced table (referenced_table)  has on the referencing table.

Syntax

<delete_rule> ::= ON DELETE CASCADE
| ON DELETE RESTRICT
| ON DELETE SET DEFAULT
| ON DELETE SET NULL

Explanation

·        No DELETE rule: deleting a row in the referenced table will fail if matching rows exist.

·        ON DELETE CASCADE: if a row in the referenced table is deleted, all of the matching rows are deleted.

·        ON DELETE RESTRICT: deleting a row in the referenced table will fails if matching rows exist.

·        ON DELETE SET DEFAULT: if a row in the referenced table is deleted, the associated DEFAULT value is assigned to each referencing column for each matching row.
A DEFAULT specification must exist for each referencing column.

·        ON DELETE SET NULL: if a row in the referenced table is deleted, a NULL value is assigned to each referencing column (referencing_column) of every matching row.
None of these referencing tables may be a NOT NULL column.

See also:

Referential CONSTRAINT Definition (referential_constraint_definition)

Column Attributes (column_attributes)