Home | About | Sematext search-lucene.com search-hadoop.com
 Search Hadoop and all its subprojects:

Switch to Threaded View
Hive, mail # user - Hive variables and assignment operator evaluations


Copy link to this message
-
Re: Hive variables and assignment operator evaluations
Edward Capriolo 2013-10-15, 16:07
hive-variables are interpreted by the CLI before the query parser. If your
using hive 0.8. you should upgrade. You can benefit hive's macro system.
On Tue, Oct 15, 2013 at 5:49 AM, Ed Soniat <[EMAIL PROTECTED]> wrote:

> Hive variables do not seem to be  evaluated by the assigned expression, so
> they seem to be macros not variables.
>
> Let us say I want to have a variable called secondsInADay and for clarity
> set it thus set secondsInADay=24*60*60;
>
> To the best of my ability to determine secondsInADay will perform the
> calculation each time it is referenced, it will not be bound to 86400 but
> will be bound to 24*60*60 and could be evaluated billions of times.
>
> This is has ramifications if I am using a date in a variable. Lets say I
> start a set of selects using a variable set thus,
>
> set priviousDay=<some code to use current date/time to calculate a
> previous date/time>
>
> And the queries referencing this previousDay variable were to execute
> across the servers day. The queries would reference different previous days
> because the variable is being evaluated in the query not at the assignment.
>
> Is this an accurate assessment and can it be avoided?
>
> Short of creating a table of values of variable evaluations, which
> wouldn't be a very pretty thing with which to join, not to mention my hive
> is pre .8 and only has overwrite so I doubt even that is feasible without
> of creating one table per variable (yuk).
>
> Thank you for considering my question.
>
> This message may contain confidential and/or privileged information.
> If you are not the addressee or authorized to receive this on behalf of
> the addressee you must not use, copy, disclose or take action based on this
> message or any information herein.
> If you have received this message in error, please advise the sender
> immediately by reply email and delete this message. Thank you.
>