<s>
The	O
SQL:1999	B-Language
standard	O
introduced	O
a	O
number	O
of	O
object	B-General_Concept
–	I-General_Concept
relational	I-General_Concept
database	I-General_Concept
features	O
into	O
SQL	B-Language
,	O
chiefly	O
among	O
them	O
structured	B-Language
user-defined	I-Language
types	I-Language
,	O
usually	O
called	O
just	O
structured	B-Language
types	I-Language
.	O
</s>
<s>
These	O
can	O
be	O
defined	O
either	O
in	O
plain	O
SQL	B-Language
with	O
CREATE	O
TYPE	O
but	O
also	O
in	O
Java	O
via	O
SQL/JRT	B-Language
.	O
</s>
<s>
SQL	B-Language
structured	B-Language
types	I-Language
allow	O
single	O
inheritance	O
.	O
</s>
<s>
Structured	B-Language
types	I-Language
are	O
supported	O
to	O
varying	O
degrees	O
in	O
Oracle	B-General_Concept
Database	I-General_Concept
,	O
IBM	B-Application
Db2	I-Application
,	O
PostgreSQL	B-Application
and	O
Microsoft	B-Application
SQL	I-Application
Server	I-Application
,	O
although	O
the	O
latter	O
only	O
allows	O
structured	B-Language
types	I-Language
defined	O
in	O
CLR	O
.	O
</s>
<s>
In	O
order	O
to	O
define	O
a	O
custom	O
structure	O
type	O
using	O
Oracle	B-General_Concept
Database	I-General_Concept
one	O
could	O
use	O
statements	O
such	O
as	O
these:Such	O
structure	O
type	O
can	O
be	O
then	O
used	O
to	O
create	O
a	O
table	O
that	O
would	O
also	O
hold	O
all	O
columns	O
defined	O
in	O
Person_Type:Custom	O
structure	O
types	O
support	O
inheritance	O
,	O
which	O
means	O
that	O
one	O
can	O
create	O
another	O
type	O
that	O
inherits	O
from	O
previous	O
.	O
</s>
<s>
Primary	B-Application
Key	I-Application
and	O
Constraints	O
should	O
be	O
defined	O
during	O
or	O
after	O
creation	O
of	O
table	O
and	O
cannot	O
be	O
defined	O
inside	O
structure	O
type	O
itself.Each	O
custom	O
structure	O
type	O
can	O
also	O
contain	O
other	O
types	O
in	O
order	O
to	O
support	O
more	O
complex	O
structures	O
:	O
</s>
