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.
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,
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)
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