Foreign keys enforce referential integrity These constraints guarantee that a row in a table order_details with a field order_id referencing an orders table will never have an order_id value that doesn't exist in the orders table Foreign keys aren't required to have a working relational database (in fact MySQL's default storage engine doesn't support FKs), but they are definitely essential to avoid broken relationships and orphan rows (ie. Referential integrity). The ability to enforce referential integrity at the database level is required for the C in ACID to stand As for your concerns regarding performance, in general there's a performance cost, but will probably be negligible.
I suggest putting in all your foreign key constraints, and only experiment without them if you have real performance issues that you cannot solve otherwise.
Foreign keys enforce referential integrity. These constraints guarantee that a row in a table order_details with a field order_id referencing an orders table will never have an order_id value that doesn't exist in the orders table. Foreign keys aren't required to have a working relational database (in fact MySQL's default storage engine doesn't support FKs), but they are definitely essential to avoid broken relationships and orphan rows (ie.
Referential integrity). The ability to enforce referential integrity at the database level is required for the C in ACID to stand. As for your concerns regarding performance, in general there's a performance cost, but will probably be negligible.
I suggest putting in all your foreign key constraints, and only experiment without them if you have real performance issues that you cannot solve otherwise.
Similar question has been answered, see stackoverflow.com/questions/1876013/ there are a lot of discussions :D.
Key value do not exist. Does not permit the deletion of any of those parent rows. Indexes corresponding to the foreign key constraints.
It acts like RESTRICT. Self-referential ON DELETE CASCADE. KEY constraints row-by-row.
Locks on child or parent records it has to look at. Immediately; the check is not deferred to transaction commit. Deleting a record that refers to itself using a foreign key.
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