A 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.
Primary key constraints. A primary key (PK) is a single column or combination of columns (called a compound key) that uniquely identifies each row in a table.
The following example to check if a primary key exists.
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_Product_ID PRIMARY KEY (ID)
)
IF OBJECT_ID('dbo.pk_Product_ID') IS NULL
ALTER TABLE PRODUCT ADD CONSTRAINT pk_Product_ID PRIMARY KEY(ID)
ELSE
PRINT 'Product table already has a primary key.'
DROP TABLE PRODUCT
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