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How do I enable delete cascade?
Edit table and columns specification by clicking … as shown in the below image.
- Select the parent table and the primary key column in the parent table.
- In the INSERT and UPDATE specifications, select Cascade for the delete rule.
- Click on Close and save the table in the designer.
How does on delete cascade work?
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.
What happens when you execute the delete statement?
If you run a DELETE statement with no conditions in the WHERE clause, all of the records from the table will be deleted. This quey will return number of records that will be deleted when you execute the DELETE statement.
What is on delete cascade and on delete Set Default?
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 DEFAULT SQL Server sets the rows in the child table to their default values if the corresponding rows in the parent table are deleted.
What will happen if you delete command without the WHERE clause?
Delete Query in SQL should always be executed with the WHERE clause to avoid unwanted data loss. Delete statement without WHERE clause will delete all the records of the table and without proper rollback mechanism, your data could be lost forever.
What will happen if the following SQL command is executed delete from customer?
The following DELETE statement deletes only one record from the main customer table. The result is your data now looks like the following. Notice that only one record was deleted instead of an entire table of records. The DELETE statement also lets you use multiple conditions in the WHERE clause.
What is the difference between on delete set null and on delete cascade?
CASCADE : Delete or update the row from the parent table and automatically delete or update the matching rows in the child table. SET NULL : Delete or update the row from the parent table and set the foreign key column or columns in the child table to NULL .