-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.
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