How does delete cascade work?

How does 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.

How do you delete parent and child records in SQL?

Two possible approaches.

1. If you have a foreign key, declare it as on-delete-cascade and delete the parent rows older than 30 days. All the child rows will be deleted automatically.
2. Based on your description, it looks like you know the parent rows that you want to delete and need to delete the corresponding child rows.

How do I change the table on delete cascade?

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 to delete rows from parent and child tables?

I would like to Delete all rows with practiceID=55 from all Parents tables and all corresponding rows from its child tables. Tables are linked with foreign key constraints (but there is no ON DELETE CASCADE). Can any one tell how to write a generalized code for removing rows from both parent and child tables.

When to delete child rows in delete Cascade?

The most typical example is that where child rows are to be deleted when parent rows are deleted, and that ON DELETE CASCADE is configured on the relevant FOREIGN KEY constraint as well: The behavior of the above configuration when a parent row is deleted is as follows:

What happens when you delete a parent in Excel?

The reason is that you delete the parent and that deletion will cascade to the child table (with the proper settings on the parent table). If you then try to delete more children in the same statement you are trying to make the system work on inexistent data and throwing out a parent that is already gone.

How does the delete orphan cascade work in SQL?

delete-orphan cascade adds behavior to the delete cascade, such that a child object will be marked for deletion when it is de-associated from the parent, not just when the parent is marked for deletion.