Apress.Expert.Oracle.Database.Architecture.9i.and.10g.Programming.Techniques.and.Solutions.Sep.2005

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CHAPTER 10 ■ DATABASE TABLES
', '123 Main Street' d', '1 Oracle Way',
, 'Va', 45678) 'Ca', 23456)
ops$tkyte@ORA10G> select name, p.home_address.city from people p;
NAME HOME_ADDRESS.CITY
----- ------------------------------
Tom Reston
We’re starting to see some of the object syntax necessary to deal with object types. For
example, in the INSERT statement we had to wrap the HOME_ADDRESS and WORK_ADDRESS with a
CAST. We cast the scalar values to be of an ADDRESS_TYPE. Another way of saying this is that
we create an ADDRESS_TYPE instance for that row by using the default constructor for the
ADDRESS_TYPE object.
Now, as far as the external face of the table is concerned, there are four columns in our
table. By now, after seeing the hidden magic that took place for the nested tables, we can
probably guess that there is something else going on. Oracle stores all object-relational data
in plain old relational tables—at the end of the day it is all in rows and columns. If we dig into
the “real” data dictionary, we can see what this table really looks like:
ops$tkyte@ORA10G> select name, segcollength
2 from sys.col$
3 where obj# = ( select object_id
4 from user_objects
5 where object_name = 'PEOPLE' )
6 /
NAME
SEGCOLLENGTH
------------------------- ------------
SYS_NC_OID$ 16
SYS_NC_ROWINFO$ 1
NAME 30
DOB 7
HOME_ADDRESS 1
SYS_NC00006$ 30
SYS_NC00007$ 30
SYS_NC00008$ 2
SYS_NC00009$ 22
WORK_ADDRESS 1
SYS_NC00011$ 30
SYS_NC00012$ 30
SYS_NC00013$ 2
SYS_NC00014$ 22
14 rows selected.
This looks quite different from what DESCRIBE tells us. Apparently, there are 14 columns in
this table, not 4. In this case, they are