Re: SQL record exists

[Vern Hamberg <vhamberg@xxxxxxxxxxx>]

Hi Rob

This is the case. It used to be called the index-only access method. I 
think now it is known as radix index probe. The OP might want to learn 
more about SQL access methods in the Database Performance and Query 
Optimization manual - the 6.1 version is at

http://publib.boulder.ibm.com/infocenter/iseries/v6r1m0/topic/rzajq/rzajq.pdf

To quote from that manual -

"If all of the columns necessary to satisfy the query request for a 
table can be found as keys of an index, then the Table Probe is not 
required and the query uses Index Only Access."

Regards
Vern

rob@xxxxxxxxx wrote:
> Thomas,
>
> If one has an index built over the customer number, and the only thing 
> read is the customer number then the entire table is not read, just the 
> index.  For example, if I do this
> select count(*), itemclass
> from itemmaster
> group by itemclass
>
> and there is an index over the itemclass then the engine reads only the 
> index and doesn't touch the physical file.
>
> I believe that is true for a Primary or unique index built into the table 
> as well.
>
>
> Rob Berendt
>