Object References (Cont.)
The VALUE DML Operator
- It returns the object stored in an object table.
- It only works on row objects.
- It returns an instance.
SQL> SELECT * FROM persons p;
NAME SSN DOB
-------------------------------- ---------- ---------
Powerpuff Girls 123456789 31-OCT-80
Kids Next Door 234567890 20-FEB-00
SQL> SELECT VALUE( p ) FROM persons p;
VALUE(P)(NAME, SSN, DOB)
---------------------------------------------------------
PERSON_TYP('Powerpuff Girls', 123456789, '31-OCT-80')
PERSON_TYP('Kids Next Door', 234567890, '20-FEB-00')
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Dangling Reference
It happens if the target object of a
REF is removed.
SQL> DELETE FROM persons p WHERE p.ssn = 123456789;
1 row deleted.
SQL> SELECT no FROM accounts WHERE acc_holder IS DANGLING;
NO
----------
1001
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The predicate
IS DANGLING returns
TRUE when applied to a deleted REF items, or
FALSE when applied to an existing REF object.
“Trees are poems the earth writes upon the sky,
We fell them down and turn them into paper,
That we may record our emptiness.”
― Kahlil Gibran
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