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)
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