unique-constraint:

1? CONSTRAINT constraint-name
2 PRIMARY KEY
2 UNIQUE
3 (
4+ ,
4 column-name
5 )

referential-constraint:

1? CONSTRAINT constraint-name
2 FOREIGN KEY (
3+ ,
3 column-name
4 ) references-clause

references-clause:

1 REFERENCES table-name
2? (
2.1+ ,
2.1 column-name
2.2 )
3! ON DELETE NO ACTION
3?
3 ON DELETE
3.1 RESTRICT
3.1 CASCADE
3.1 SET NULL
3.1 SET DEFAULT
3.1.1! ON UPDATE NO ACTION
3.1.1?
3.1.1 ON UPDATE RESTRICT
3.1.2 (1) 


check-constraint:

1? CONSTRAINT constraint-name
2 CHECK ( check-condition )