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From: "Harry331" <harryooopotter@hotmail.com>
Newsgroups: comp.databases.oracle.misc
Subject: Re: update a date field with fixed date but random hours/minutes
Date: 3 Mar 2006 15:14:34 -0800
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Xref: dp-news.maxwell.syr.edu comp.databases.oracle.misc:125692

Mark C. Stock wrote:
[snip]
> this is all you need:
>
>
> update study s
>   set s.my_exam_date_time =
>   to_date(to_char(sysdate -1,'YYYY-MM-DD')
>               ||' '
>               ||trunc(dbms_random.value(0,24))
>               ||':'
>               ||trunc(dbms_random.value(0,60)),
>           'YYYY-MM-DD hh24:mi')
>   where
>         s.my_exam_date_time >= date '2006-01-01'
>   and   s.my_exam_date_time < date '2006-03-01'
>
>
> so, compary this with your code and figure out what parts of your code were
> unnecessary, then go buy tom kyte's book and study it before you do much
> more SQL programming... you're getting it to work, but you'll do better if
> you get a better feel for how the language is best designed to work

I now understand the effect of subqueries which made my previous query
not working.

Thanks for your advices.