Can set NULL be used with on delete command?
Can set NULL be used with on delete command?
SET NULL. It is used in conjunction with ON DELETE or ON UPDATE. It means that the child data is set to NULL when the parent data is deleted or updated.
What is the difference between on delete cascade and on delete set NULL?
ON DELETE CASCADE : SQL Server deletes the rows in the child table that is corresponding to the row deleted from the parent table. 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.
How do you delete NULL records in SQL?
Use the delete command to delete blank rows in MySQL. delete from yourTableName where yourColumnName=’ ‘ OR yourColumnName IS NULL; The above syntax will delete blank rows as well as NULL row.
How do I use the default delete set?
SET DEFAULT: Using the SET DEFAULT option of the ON UPDATE and ON DELETE clauses specifies that, if the referenced values in the parent table are updated or deleted, the related values in the child table with FOREIGN KEY columns will be set to its default value.
What is on delete restrict in SQL?
The ON DELETE clause says that if a particular primary key ID value in the CUSTOMERS table is deleted, this action shall be prevented (this is the “restrict” part) if there is any row in the ORDERS table which has a foreign key that matches the value of the CUSTOMER table ID value.
What is on delete cascade in SQL?
ON DELETE CASCADE constraint is used in MySQL to delete the rows from the child table automatically, when the rows from the parent table are deleted. For example when a student registers in an online learning platform, then all the details of the student are recorded with their unique number/id.
Is it good to use on delete cascade?
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 is difference between Cascade and set NULL?
CASCADE: Updates or deletes records from the child table automatically when updating or deleting a record from the parent table. SET NULL: Set to null the value of the field in the child table when updating or deleting the parent table record.
How do you handle NULL values in SQL Server?
As we stated earlier, SQL Server offers some functions that help to handle NULL values. ISNULL(): The ISNULL() function takes two parameters and it enables us to replace NULL values with a specified value. The expression parameter indicates the expression which we want to check NULL values.
What does on delete No action do?
ON DELETE NO ACTION (which is the same as omitting the ON DELETE clause) will actively prevent deletion of a parent row if it is referenced by any child table, not passively allow it to be deleted without affecting child rows.
What is on delete cascade and on delete restrict?
1) ON DELETE CASCADE means if the parent record is deleted, then any referencing child records are also deleted. ON UPDATE defaults to RESTRICT, which means the UPDATE on the parent record will fail. 2) ON DELETE action defaults to RESTRICT, which means the DELETE on the parent record will fail.