How does on delete cascade work?

Use the ON DELETE CASCADE option to specify whether you want rows deleted in a child table when corresponding rows are deleted in the parent table. If you do not specify cascading deletes, the default behavior of the database server prevents you from deleting data in a table if other tables reference it.

What is on delete cascade and on delete Set Default?

It means that the child data is set to NULL when the parent data is deleted or updated. SET DEFAULT. It is used in conjunction with ON DELETE or ON UPDATE. It means that the child data is set to their default values when the parent data is deleted or updated.

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.

Can we delete primary key from a table using delete?

How can we remove PRIMARY KEY constraint from a column of an existing MySQL table? We can remove PRIMARY KEY constraint from a column of an existing table by using DROP keyword along with ALTER TABLE statement.

How do you use delete cascade at the table of time?

Edit table and columns specification by clicking … as shown in the below image.

1. Select the parent table and the primary key column in the parent table.
2. In the INSERT and UPDATE specifications, select Cascade for the delete rule.
3. Click on Close and save the table in the designer.

What is on delete cascade on update cascade?

ON UPDATE CASCADE ON DELETE CASCADE means that if you UPDATE OR DELETE the parent, the change is cascaded to the child. This is the equivalent of AND ing the outcomes of first two statements.

How we set and remove primary key in a table?

The syntax to drop a primary key in MySQL is: ALTER TABLE table_name DROP PRIMARY KEY; table_name. The name of the table to modify.

Which command is used to delete the data from the table without deleting the table structure?

TRUNCATE Command is a Data Definition Language operation. It is used to remove all the records from a table. It deletes all the records from an existing table but not the table itself. The structure or schema of the table is preserved.

Where can I use delete cascade?

Use the ON DELETE CASCADE option if you want rows deleted from the child table when the DELETE or MERGE statement removes corresponding rows from the parent table.

What is Cascade delete in access?

Cascade Delete – this option means that if you delete a record from one table, corresponding records in the other table are also deleted. Restrict Delete – this option means that if you attempt to delete a record from one table but there is a corresponding record in the other table, the delete operation is not allowed.

How delete primary key row in SQL?

Use SQL Server Management Studio

1. In Object Explorer, expand the table that contains the primary key and then expand Keys.
2. Right-click the key and select Delete.
3. In the Delete Object dialog box, verify the correct key is specified and select OK.

How do you remove a primary key in access?

First we click the home tab and click the view tab, and then select the design view.

1. Select the roe whose the primary key remove.
2. On the Design tab, in the Tools group, click Primary Key.
3. The key indicator is removed from the field or fields that we previously specified as the primary key.

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