Tables in memory (Nested tables ?)

Question

For performance reasons, I would like to insert, update, etc...
a table in memory. Can I use a nested table as if it was a
normal table ? Can I do updates on nested tables with values
from normal database tables ??
Statement like : Update <nested-table> set <nested-
table>.x=<value> where <nested-table>.y = <normal-table>.y
Thanks for a quick response.

Answer 1

The answer is yes and no.
A nested table is a "collection" and can be referenced in a SQL
statement using the pseudo-functions THE, CAST, MULTISET and
TABLE. The nested table and varray collections can be a column
in a database table (Oracle8) and are persistent. SQL
statements cannot act on memory held nested tables, varray and
index-by collections, which are transient. Index-by collections
are same as the older PL/SQL tables.
SQL statements cannot operate directly on transient collections.
For speed you can define an index-by collection as a table of
rowtype, and move data back and forth from database tables and
memory held tables using SQL. Records and index-by tables are
more efficient in Oracle 8 than in Oracle 7
In PL/SQL you can use replacement (:=) on the record or
record.column of the rowtype index-by collection. The downside
is you have to keep track of your own indexing which is only
BINARY_INTEGER, no SELECT, UPDATE, INSERT using FROM and WHERE
on transient collections. This works in Oracle 7 also.
Good Luck.