This article is tagged with: Sql foreign key and mysql

sql foreign key

# A foreign key is essentially a reference to a primary
# key in another table.
# A Simple table of Users,
CREATE TABLE users(
userId INT NOT NULL,
username VARCHAR(64) NOT NULL,
passwd VARCHAR(32) NOT NULL,
PRIMARY KEY(userId);
);
# Lets add a LEGIT user!
INSERT INTO users VALUES(1000,"Terry","Teabagface$2");
# We will create an order table that holds a reference
# to an order made by our Terry
CREATE TABLE orders(
orderId INT NOT NULL,
orderDescription VARCHAR(255),
ordererId INT NOT NULL,
PRIMARY KEY(orderId),
FOREIGN KEY (ordererId) REFERENCES users(userId)
);
# Now we can add an order from Terry
INSERT INTO orders VALUES(0001,"Goat p0rn Weekly",1000);
# Want to know more about the plight of Goats?
# See the link below

alter table foriegn key sql

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

alter table add column and foreign key mysql

ALTER TABLE database.table
ADD COLUMN columnname INT DEFAULT(1),
ADD FOREIGN KEY fk_name(fk_column) REFERENCES reftable(refcolumn) ON DELETE CASCADE;

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;


sql foreign key

CREATE TABLE orders (
id int NOT NULL,
user_id int,
product_id int,
PRIMARY KEY (id),
FOREIGN KEY (user_id) REFERENCES users(id),
FOREIGN KEY (product_id) REFERENCES products(id)
);

create table foreign key

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

This article is tagged with: Sql foreign key and mysql