If Primary Key Exists

SELECT * FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS WHERE  CONSTRAINT_TYPE = 'PRIMARY KEY' AND TABLE_NAME = 'user_career_pref_date' AND TABLE_SCHEMA ='dbo'

if not exists(SELECT * FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS WHERE  CONSTRAINT_TYPE = 'PRIMARY KEY' AND TABLE_NAME = 'user_career_pref_date' AND TABLE_SCHEMA ='dbo' )

begin

ALTER TABLE [dbo].[user_career_pref_date]

    ADD CONSTRAINT [PK_user_career_pref_date] PRIMARY KEY CLUSTERED ([user_id] ASC, [question_id] ASC) WITH (ALLOW_PAGE_LOCKS = ON, ALLOW_ROW_LOCKS = ON, PAD_INDEX = OFF, IGNORE_DUP_KEY = OFF, STATISTICS_NORECOMPUTE = OFF);

end