You are viewing a plain text version of this content. The canonical link for it is here.

Posted to dev@drill.apache.org by Norris Lee <no...@simba.com> on 2014/10/24 01:42:15 UTC

Query optimization and obtaining metadata

Hi,

I have a question about getting column metadata in the most efficient manner.

Is it more efficient to use LIMIT 1 or WHERE 0=1? Or is there an even better way?
Does Drill prune the query out completely if it recognizes a false predicate?

Thanks,
Norris

Re: Query optimization and obtaining metadata

Posted by Bob Rumsby <br...@maprtech.com>.

There is a DESCRIBE command, which is covered in the Drill Tutorial.

Bob

On Thu, Oct 23, 2014 at 4:42 PM, Norris Lee <no...@simba.com> wrote:

> Hi,
>
> I have a question about getting column metadata in the most efficient
> manner.
>
> Is it more efficient to use LIMIT 1 or WHERE 0=1? Or is there an even
> better way?
> Does Drill prune the query out completely if it recognizes a false
> predicate?
>
> Thanks,
> Norris
>

Re: Query optimization and obtaining metadata

Posted by Jacques Nadeau <ja...@apache.org>.

For tables that don't return metadata with describe, limit 0 is fastest.
We haven't yet implemented a check yet for a false expression.

On Thu, Oct 23, 2014 at 4:42 PM, Norris Lee <no...@simba.com> wrote:

> Hi,
>
> I have a question about getting column metadata in the most efficient
> manner.
>
> Is it more efficient to use LIMIT 1 or WHERE 0=1? Or is there an even
> better way?
> Does Drill prune the query out completely if it recognizes a false
> predicate?
>
> Thanks,
> Norris
>