FOREIGN KEY constraint in sql server

FOREIGN KEY- This constraints responsible to uniquely identified a rows or records to another table.

Example-

Following table structure can clear your concept of foreign key constraint.

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,

DISCRIPTION 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 foreign key constraint to existing table use following query.

ALTER TABLE PRODUCT_IMAGE ADD FOREIGN KEY (PRODUCT_ID) REFERENCES PRODUCT(ID)

Comments

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