How do you add on delete cascade to a foreign key constraint?
Alter table to remove Foreign Key or add DELETE CASCADE (MySQL)
- Step 1 : Get the Foreign Key Name. SHOW CREATE TABLE tableName;
- Step 2: Drop the Foreign Key. Alter table tableName drop foreign key FK4C5B93445F11A0B7.
- Step 3: Now add the foreign key constraint back again, this time with ON DELETE CASCADE.
What is the meaning of On delete cascade in foreign key?
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 happens when someone tries to delete an entry of a table that has referential integrity constraint?
If a referential constraint is violated, the DELETE operation fails. The action to be taken on dependent tables when a DELETE is performed on a parent table depends on the delete rule specified for the referential constraint. If no delete rule was defined, the DELETE NO ACTION rule is used.
How to delete rows that contain foreign keys?
You database engine will take care of deleting the corresponding referencing records. You can alter a foreign key constraint with delete cascade option as shown below. This will delete chind table rows related to master table rows when deleted.
When to delete cascade in SQL Server foreign key?
DELETE CASCADE: When we create a foreign key using this option, it deletes the referencing rows in the child table when the referenced row is deleted in the parent table which has a primary key.
How to remove multiple rows from a table in Excel?
If you have multiply rows to delete and you don’t want to alter the structure of your tables you can use cursor. 1-You first need to select rows to delete (in a cursor) 2-Then for each row in the cursor you delete the referencing rows and after that delete the row him self.
How to delete rows from a referencing table?
First, as a one-time data-scrubbing exercise, delete the orphaned rows e.g. DELETE FROM ReferencingTable WHERE NOT EXISTS ( SELECT * FROM MainTable AS T1 WHERE T1.pk_col_1 = ReferencingTable.pk_col_1 );