FOREIGN KEY- This constraint responsible for uniquely identified rows or records to another table.
Example-
Following table structure can clear your concept of foreign key constraints.
Product Table
CREATE TABLE PRODUCT
(
ID INT NOT NULL IDENTITY(1,1),
SKU VARCHAR(20) NOT NULL,
TITLE VARCHAR(200) NOT NULL,
PRICE MONEY NOT NULL,
DESCRIPTION VARCHAR(2000) NULL,
DTCREATE DATETIME NULL
CONSTRAINT pk_ID PRIMARY KEY (ID)
)
Product Order Table
CREATE TABLE PRODUCT_IMAGE
(
ID INT NOT NULL IDENTITY(1,1),
PRODUCT_ID INT NOT NULL REFERENCES PRODUCT(ID),
IMGURL VARCHAR(200) NOT NULL ,
DTCREATE DATETIME
)
To create a foreign key constraint to existing table use following query.
ALTER TABLE PRODUCT_IMAGE ADD FOREIGN KEY (PRODUCT_ID) REFERENCESPRODUCT(ID)
