What does on delete cascade do MySQL?

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.

When should you use on delete cascade?

Use cascade delete where you would want the record with the FK to be removed if its referring PK record was removed. In other words, where the record is meaningless without the referencing record. I find cascade delete useful to ensure that dead references are removed by default rather than cause null exceptions.

Is on delete cascade good or bad?

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.

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What does on delete cascade does?

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 the difference between on delete cascade and on delete set null?

CASCADE : Delete or update the row from the parent table and automatically delete or update the matching rows in the child table. Both ON DELETE CASCADE and ON UPDATE CASCADE are supported. … 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 .

What is the purpose on delete cascade deletes the dependent rows?

ON DELETE CASCADE clause in MySQL is used to automatically remove the matching records from the child table when we delete the rows from the parent table. It is a kind of referential action related to the foreign key.

What does on delete No action do?

The ON DELETE SET NULL action allows data that references the parent key to be deleted, but not updated. When referenced data in the parent key is deleted, all rows in the child table that depend on those parent key values have their foreign keys set to null.

What does cascading over mean?

: to fall, pour, or rush in or as if in a cascade The water cascaded over the rocks. Her hair cascaded down around her shoulders. transitive verb.

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What does on update cascade mean in SQL?

In that case, ON UPDATE CASCADE would allow you to change the primary key value and any tables that have foreign key references to the value will be changed accordingly.

What does Cascade mean in phpmyadmin?

CASCADE : CASCADE will propagate the change when the parent changes. If you delete a row, rows in constrained tables that reference that row will also be deleted, etc. RESTRICT : RESTRICT causes you can not delete a given parent row if a child row exists that references the value for that parent row.

How do I use delete cascade?

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 does an on delete cascade clause imply in a foreign key constraint in a MySQL create table statement?

In MySQL, foreign key constraints are checked immediately, so NO ACTION and RESTRICT are the same.) ON DELETE CASCADE causes matching child records to be deleted when the corresponding parent record is deleted.

What is on delete restrict?

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.

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What happens if the on delete cascade clause is set?

A foreign key with cascade delete means that if a record in the parent table is deleted, then the corresponding records in the child table will automatically be deleted.

What is on delete cascade in SQL explain clearly with example?

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 does on update restrict do?

1 Answer. RESTRICT prevents the action from happening if there’s any foreign keys that rely on the field that’s being changed.