-- On Create CREATE TABLE tableName ( ID INT, SomeEntityID INT, PRIMARY KEY (ID), FOREIGN KEY (SomeEntityID) REFERENCES SomeEntityTable(ID) ON DELETE CASCADE ); -- On Alter, if the column already exists but has no FK ALTER TABLE tableName ADD FOREIGN KEY (SomeEntityID) REFERENCES SomeEntityTable(ID) ON DELETE CASCADE; -- Add FK with a specific name -- On Alter, if the column already exists but has no FK ALTER TABLE tableName ADD CONSTRAINT fk_name FOREIGN KEY (SomeEntityID) REFERENCES SomeEntityTable(ID) ON DELETE CASCADE;

mysql add foreign key

ALTER TABLE Orders ADD CONSTRAINT FK_PersonOrder FOREIGN KEY (PersonID) REFERENCES Persons(PersonID);

add constraint fk

CREATE TABLE parent ( id INT NOT NULL, PRIMARY KEY (id) ) ENGINE=INNODB; CREATE TABLE child ( id INT, parent_id INT, INDEX par_ind (parent_id), FOREIGN KEY (parent_id) REFERENCES parent(id) ON DELETE CASCADE ) ENGINE=INNODB;

foreign key mySql

CREATE TABLE Orders ( OrderID int NOT NULL, OrderNumber int NOT NULL, PersonID int, PRIMARY KEY (OrderID), FOREIGN KEY (PersonID) REFERENCES Persons(PersonID) );

create table mysql with foreign key

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