sql server foreign key constraint code example
Example 1: mysql add foreign key
-- 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;
Example 2: sql foreign key
CREATE TABLE users(
userId INT NOT NULL,
username VARCHAR(64) NOT NULL,
passwd VARCHAR(32) NOT NULL,
PRIMARY KEY(userId);
);
INSERT INTO users VALUES(1000,"Terry","Teabagface$2");
CREATE TABLE orders(
orderId INT NOT NULL,
orderDescription VARCHAR(255),
ordererId INT NOT NULL,
PRIMARY KEY(orderId),
FOREIGN KEY (ordererId) REFERENCES users(userId)
);
INSERT INTO orders VALUES(0001,"Goat p0rn Weekly",1000);