Editing Foreign key (section)

=== RESTRICT ===
A value cannot be updated or deleted when a row exists in a referencing or child table that references the value in the referenced table.

Similarly, a row cannot be deleted as long as there is a reference to it from a referencing or child table.

To understand RESTRICT (and CASCADE) better, it may be helpful to notice the following difference, which might not be immediately clear. The referential action CASCADE modifies the "behavior" of the (child) table itself where the word CASCADE is used. For example, ON DELETE CASCADE effectively says "When the referenced row is deleted from the other table (master table), then delete ''also from me''". However, the referential action RESTRICT modifies the "behavior" of the master table, ''not'' the child table, although the word RESTRICT appears in the child table and not in the master table! So, ON DELETE RESTRICT effectively says: "When someone tries to delete the row from the other table (master table), prevent deletion ''from that other table'' (and of course, also don't delete from me, but that's not the main point here)."

RESTRICT is not supported by Microsoft SQL 2012 and earlier.