SQL Server 2008 Add constraint

ALTER TABLE Student--PRIMARY KEY constraint
ADD CONSTRAINT Pk_stuno PRIMARY KEY (Studentno)

ALTER TABLE Student--UNIQUE constraint (ID number unique)
ADD CONSTRAINT uq_stuid UNIQUE (Identitycard)

ALTER TABLE Student--Default constraint (address unknown)
Add CONSTRAINT df_stuaddress DEFAULT (' address unknown ') for address

ALTER TABLE Student-Check constraint (date of birth is from January 1, 1980 onwards)
ADD CONSTRAINT ck_stuborndate CHECK (borndate>= ' 1980-1-1 ')

ALTER TABLE Student--Add foreign KEY constraint
ADD CONSTRAINT Fk_grade
FOREIGN KEY (Gradeid) REFERENCES Grade (Gradeid)
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SQL Server 2008 Add constraint