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.

Table of Contents

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.

What happens if the on delete cascade clause is set?

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 set null in MySQL?

In MySQL, a NULL value means unknown. A NULL value is different from zero ( 0 ) or an empty string ” . A NULL value is not equal to anything, even itself. If you compare a NULL value with another NULL value or any other value, the result is NULL because the value of each NULL value is unknown.

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 set NULL in MySQL?

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.

How do I DELETE a row in MySQL?

To delete rows in a MySQL table, use the DELETE FROM statement: DELETE FROM products WHERE product_id=1; The WHERE clause is optional, but you’ll usually want it, unless you really want to delete every row from the table.

How do you set a value to NULL in SQL?

If you’ve opened a table and you want to clear an existing value to NULL, click on the value, and press Ctrl + 0 .

How do you use Restrict on delete?

Where do I put the 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 do I use on delete cascade and update cascade in MySQL?

First, we need to use the ALTER TABLE statement to add the ON UPDATE CASCADE clause in the table Payment as below:

ALTER TABLE Payment ADD CONSTRAINT `payment_fk`
FOREIGN KEY(emp_id) REFERENCES Employee (emp_id) ON UPDATE CASCADE;

How do I delete a specific row in SQL?

SQL DELETE Statement

DELETE FROM table_name WHERE condition;
Example. DELETE FROM Customers WHERE CustomerName=’Alfreds Futterkiste’;
DELETE FROM table_name;
Example. DELETE FROM Customers;