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Check if a primary key constraint exists in SQL server

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.

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 primary key'

DROP TABLE PRODUCT