Answer / atikullah

No, I think unique constraint contain no duplicate value in
a column. There are only contains unique value

Answer / rammohan176

yes Unique constraint accept more than one null.... because null is always not equal to another null value.i.e null<>null.
if any body have doubt please check this
CREATE TABLE TEST1 ( ENO NUMBER CONSTRAINT EU UNIQUE,
NAME1 VARCHAR2(10))

INSERT INTO TEST1 (NAME1) VALUES('RAM')

INSERT INTO TEST1 (NAME1) VALUES('KARTHIK')
INSERT INTO TEST1 (NAME1) VALUES('SANTHOSH')
INSERT INTO TEST1 (NAME1) VALUES('SANDY')

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