PRIMARY KEY- The 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 has a unique identity.
Example-
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,
DESCRIPTION VARCHAR(2000) NULL,
DTCREATE DATETIME NULL
CONSTRAINT pk_ID PRIMARY KEY (ID)
)
If a table already exists, then use the following query.
ALTER TABLE PRODUCT ADD CONSTRAINT pk_products_pid PRIMARY KEY(ID)
