RE: DBA Question

["Carel Teijgeler" <coteijgeler@xxxxxxxxx>]

I think this should be added:

With a view or a LF you can get a subset of the columns/fields from a 
table/file. You do not have to select all columns/fields.

Regards,
Carel Teijgeler

*********** REPLY SEPARATOR  ***********

On 17-6-05 at 22:17 Joe Pluta wrote:

>>From a layman's point of view, you can think of it this way:
>
>1. An INDEX allows you to order records
>2. A VIEW allow you to select records
>3. A logical file allows both
>
>It's a bit more complicated than that, of course.  But in general an
>index can only determine the order of records (it can also be used to
>impose uniqueness on a key), while a view can only define the records
>and fields to be selected.
>
>A logical file, on the other hand, allows both ordering and selection.
>It also has the ability to specify the maintenance mode, allowing you to
>keep the index current at all times (small overhead on every write) or
>to defer the build of the index to when it is needed (large overhead on
>open, or at IPL).
>
>Logical files are more record-oriented and allow positioning by key,
>including partial key, as well as easy update of individual records.
>SQL cursors over indexes and views allow update of the current record,
>but also allow a single statement to update multiple records.  However,
>positioning the cursor within an index or a view is not as flexible as
>positioning within a logical file.
>
>Different databases have different implementations of indexes, views and
>indexes over view.  For example, SQL Server creates a persistent B-tree
>index when you create an index over a view.  Thus, performance for
>various combinations of index and view are somewhat dependent on the
>database.
>
>Joe