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What is function of on update cascade clause?
CASCADE. It is used in conjunction with ON DELETE or ON UPDATE. It means that the child data is either deleted or updated when the parent data is deleted or updated.
What is on update cascade in SQL Server?
ON UPDATE CASCADE : SQL Server updates the corresponding rows in the child table when the rows in the parent table are updated. ON UPDATE SET NULL : SQL Server sets the rows in the child table to NULL when the corresponding row in the parent table is updated.
What does on Update no action do?
In the case of a dependent row, the NO ACTION update rule is implicit when a foreign key is specified. NO ACTION means that a non-null update value of a foreign key must match some value of the parent key of the parent table when the update statement is completed.
How to use cascade on delete and on update?
ON DELETE RESTRICT: we can not delete the row from the parent table if it has any referenced row with the same id. ON DELETE NO ACTION: In this cascade, there is no referential delete action performed. The same Cascade is also applicable for ON UPDATE cascade just replace DELETE to UPDATE and remain syntax will be same.
When to use ” on update Cascade ” SQL Server?
ON DELETE SET NULL: SQL Server sets the rows in the child table to NULL if the corresponding rows in the parent table are deleted. To execute this action, the foreign key columns must be nullable. ON DELETE SET DEFAULT: SQL Server sets the rows in the child table to their default values if the corresponding rows in the parent table are deleted.
When to update cascade in a foreign key?
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. We will be discussing the following topics in this article: Creating DELETE and UPDATE CASCADE rule in a foreign key using SQL Server management studio
When to use ” on update cascade ” when parent is not updatable?
This should be no problem. This means that “ON UPDATE CASCADE” will do the same thing when id of the parent is updated? If (1) is true, it means that there is no need to use “ON UPDATE CASCADE” if parent.id is not updatable (or will never be updated) like when it is AUTO_INCREMENT or always set to be TIMESTAMP.