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Is on delete cascade bad?
Cascading deletes should not cause unexpected loss of data. If a delete requires related records to be deleted, and the user needs to know that those records are going to go away, then cascading deletes should not be used.
What happens if Restrict is selected on update and on delete?
RESTRICT means that any attempt to delete and/or update the parent will fail throwing an error. This is the default behaviour in the event that a referential action is not explicitly specified. For an ON DELETE or ON UPDATE that is not specified, the default action is always RESTRICT`.
What is the purpose of on update cascade in SQL?
UPDATE CASCADE: When we create a foreign key using UPDATE CASCADE the referencing rows are updated in the child table when the referenced row is updated in the parent table which has a primary key.
When to use Cascade update vs Cascade delete?
You should not use Cascade Delete if you are preserving history or using a “soft/logical delete” where you only set a deleted bit column to 1/true. Cascade Update may make sense when you use a real key rather than a surrogate key (identity/autoincrement column) across tables.
What does on delete Cascade mean in MySQL?
ON DELETE CASCADE is an optional clause in a foreign key declaration. So it goes with the foreign key declaration. (Meaning, in the “child” table.) …it could mean delete the Parent record when the Child record is deleted, or it could mean delete the Child record when the Parent is deleted.
When does Cascade delete just once in PostgreSQL?
CASCADE specifies that when a referenced row is deleted, row (s) referencing it should be automatically deleted as well. I took Joe Love’s answer and rewrote it using the IN operator with sub-selects instead of = to make the function faster (according to Hubbitus’s suggestion):
What is the syntax for on delete, cascade, on foreign delete?
I wish the syntax was ON PARENT DELETE, CASCADE, ON FOREIGN DELETE, CASCADE or something similar to remove the ambiguity. Does anyone have any mnemonics for remembering this? If you like the Parent and Child terms and you feel they are easy to be remembered, you may like the translation of ON DELETE CASCADE to Leave No Orphans!