Multi table operation - foreign key cascade operation

• Catalog

  Cascade update and cascade delete of foreign key

  What is cascading updates

  What is cascade deletion

  Add cascading updates

  Add cascade delete

  Add cascade update and cascade delete at the same time

  Examples demonstrate

  Add a foreign key constraint , Add cascade update and cascade delete at the same time

  Test after adding

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• Cascade update and cascade delete of foreign key

• What is cascading updates

• When I want to modify the data in the main table
• I expect that the associated data from the table will also be modified

• What is cascade deletion

• When I want to delete the data in the main table
• I expect that the associated data from the table will also be deleted

• Add cascading updates

• alter table Table name add
• constraint Foreign key name foreign key ( Foreign key column name of this table ) references Main table name ( Primary key column name )
• on update cascade;

• Add cascade delete

• alter table Table name add
• constraint Foreign key name foreign key ( Foreign key column name of this table ) references Main table name ( Primary key column name )
• on delete cascade;

• Add cascade update and cascade delete at the same time

• alter table Table name add
• constraint Foreign key name foreign key ( Foreign key column name of this table ) references Main table name ( Primary key column name )
• on update cascade on delete cascade;

• Examples demonstrate

• Add a foreign key constraint , Add cascade update and cascade delete at the same time

• 

• --  Add a foreign key constraint , Add cascade update and cascade delete at the same time 
  ALTER TABLE ouser ADD CONSTRAINT ou FOREIGN KEY (uid) REFERENCES user(id)
  ON UPDATE CASCADE ON DELETE CASCADE;

• Test after adding

• Original form information
• 
• Make changes
• 
• 

• --  The user Li Si id Change it to 3,ouser In the table uid Also automatically modify 
  UPDATE user SET id=3 WHERE id=2;

• 
• 

• --  Delete the user Li Si ,ouser The related ownership in the table is also automatically deleted 
  DELETE FROM user WHERE id=3;