How do I delete on Cascade in MySQL?

Where is Cascade delete in MySQL?

Alter table to remove Foreign Key or add DELETE CASCADE (MySQL)

  1. Step 1 : Get the Foreign Key Name. SHOW CREATE TABLE tableName; …
  2. Step 2: Drop the Foreign Key. Alter table tableName drop foreign key FK4C5B93445F11A0B7. …
  3. Step 3: Now add the foreign key constraint back again, this time with ON DELETE CASCADE.

How does cascade delete work?

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. This is called a cascade delete in SQL Server.

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.

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.
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What is on update cascade in mysql?

The ON UPDATE CASCADE tells the database that when an update occurs on the referenced column from the parent table (“ id ”), it must automatically update the matching rows in the child table (“ books ”) with the new value.

When should I 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.

When should you use on delete cascade?

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 cascade delete option used for?

Notes: Cascade Delete option means that if a record from one table is deleted, corresponding records in the other table are also deleted.

What is Cascade on delete in 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.

Can a foreign key be null?

A foreign key containing null values cannot match the values of a parent key, since a parent key by definition can have no null values. However, a null foreign key value is always valid, regardless of the value of any of its non-null parts. … A foreign key value is null if any part is null.

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What is on delete Set null?

A foreign key with “set null on delete” means that if a record in the parent table is deleted, then the corresponding records in the child table will have the foreign key fields set to NULL. The records in the child table will not be deleted in SQL Server.

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