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See Oracle Collections, Nested Tables and VARRAY Columns



Oracle collections are a non-relational extension of Oracle that allow non first-normal form representation of data, either via repeating groups of table columns addressed with subscripts (e.g. select test_score(3) from student;) or via the non-relation "nested table" construct.

Below, Lewis Cunningham has an excellent overview and examples of these Oracle collection features:

http://blogs.ittoolbox.com/oracle/guide/archives/006003.asp 

Cunningham shows examples of VARRAY table definition and queries:

SQL> SELECT * FROM person
2 /

NAME  DOB
------------------------------ ---------
ADDRESS_V
---------------------------------------------------------------
ADDRESS_N
---------------------------------------------------------------
Lewis 01-JAN-60
ADDRESSES_V('Line 1', 'Line 2', 'Line 3')
ADDRESSES_N('Line 1', 'Line 2', 'Line 3')


Cunningham also shows Oracle nested table definitions and usage. The author concludes about the choice between nested tables and VARRAY tables:

"Now I guess we should talk about when to use a particular type of collection. In PL/SQL, for the most part, it's a matter of preference. If you know you have a maximum, use VARRAY. The choice between Nested Table and Associative Table is not as clear cut. In general, I use Nested Table instead of Associative Tables unless I am indexing the array with a VARCHAR2.

In SQL, it's a different subject. Of course, you cannot use an Associative table at all in SQL so your choices are down to Nested Table or Varray. I rarely, if ever, use nested tables or varrays in a relational table. I prefer to create a normal table and use foreign keys."


 

 
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