PRIMARY KEY- Primary key constraint is a combination of a NOT NULL constraint and a UNIQUE constraint. This constraint ensures that the specific column for a table have an unique identity.
Following we create a table PRODUCT in which column ID has primary key constraints.
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)
If table already exits then use following query.
ALTER TABLE PRODUCT ADD CONSTRAINT pk_products_pid PRIMARY KEY(ID)