Re: UNION or UNION ALL - which faster

From: Gerd Kock <info_at_gerd-kock.de>
Date: Sat, 25 Mar 2000 17:41:28 GMT
Message-ID: <38dcf996.1682371@news.btx.dtag.de>

On Sat, 25 Mar 2000 13:38:42 GMT, "my" <mohamed.yusuf_at_sympatico.ca> wrote:

>hi everybody,
>
>I'm hitting 5 tables with millions of records using operator UNION or UNION
>ALL. both takes hrs to get the result - I'm not worried since UNION ALL
>returns dublicates as well. Can anybody tell me the best way or alternative
>ways that makes faster.
>
>

is there a where clause?
are there indexes on the tables?
do you need all the data?
are the tables partitioned?
is the data model right?
is the instance tuned?
is the server well sized?

performance tuning is a wide field and there can not be a global answer Received on Sat Mar 25 2000 - 11:41:28 CST