[web2py] what does unique=True do?

[apple]

The following code in a model results in two rows with the name
"test". So what does unique=True do?

db.define_table("view",
        Field('name', requires=[IS_NOT_EMPTY(), IS_NOT_IN_DB(db,
'view.name')], unique=True),
        Field('includedfields'),
        signature)
db.view.insert(name="test")
db.view.insert(name="test")
db.commit()